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When  you  leave,  please  leave  this  book 

Because  it  has  been  said 
"Ever  thing  comes  t'  him  who  waits 

Except  a  loaned  book." 


Avery  Architectural  and  Fine  Arts  Library 
Gift  of  Seymour  B.  Durst  Old  York  Library 


THOS.  V.  PAUL 
PHILA  PA. 


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TUNNELING 


R    THE 


Hudson    River: 


BEING 

A  DESCRIPTION  OF  THE  OBSTACLES  ENCOUNTERED,  TIIE  EXPEMENCE 

GAINED,  THE  SUCCESS  ACHIEVED,  AND  THE  PLANS  FINALLY 

ADOPTED  FOR  RAPID  AND  ECONOMICAL 

PROSECUTION  OF  TIIE  WORK. 


BY 

S.    D.    Y.    BUEE,    A.M. 


3Uustrateo  by  TKHorfeincj  Drawings  of  all  Details. 


T  WEXTY-SE  YEN  PL  A  TES. 


NEW  YORK: 

JOHN   WILEY    &    SONS, 
15  Astoe  Place. 

1885. 


COPTBIOHT, 

JOHN  WILEY  ft  SONS 

1SS5. 


PREFACE 


Tiik  general  plans  according  to  which  some  twenty-five  hundred 
feet  of  the  Hudson  River  tunnel  have  been  built  are  new  :  in  exe- 
cuting them  novel  methods  have  been  introduced — great  obstacles 
have  been  surmounted — most  valuable  experience  has  been  gained. 
By  their  aid  a  daily  average  of  three,  four,  and  sometimes  over 
five  feet  of  tunnel  was  completed  during  shorter  or  longer  periods 
of  time ;  and  when  the  heading  was  more  than  one  thousand  feet 
from  the  shore  an  average  of  three  and  one-third  feet  of  tunnel  was 
built  each  day  for  more  than  two  hundred  consecutive  days — a  per- 
formance in  engineering  which  far  surpasses  anything  heretofore 
accomplished  through  like  material.  So  far  some  $1,100,000  have 
been  expended.  Considering  the  great  size  of  the  tunnel,  the 
character  of  the  material  passed  through,  and  the  depth  under 
water,  this  is  one  of  the  cheapest,  if  not  the  cheapest,  specimens  of 
submarine  tunneling  ever  accomplished,  and  this  in  the  face  of  the 
facts  that  many  stages  of  the  work  were  necessarily  experimental, 
that  there  were  several  serious  delays — one  caused  by  the  accident 
— and  that  there  were  constant  hindrances  to  rapid  and  economical 
progress. 

In  the  following  pages  the  aim  has  been  to  plainly,  concisely, 
and  yet  fully  describe  every  stage  of  the  work.  Although  the  fun- 
damental idea  embodying  the  use  of  compressed  air  was  always 
adhered  to,  yet  those  which  might  be  termed  auxiliary  plans,  or 


4  PREFACE. 

methods  of  doing  certain  pieces  of  work  which  presented  features 
peculiarly  their  own,  were  modified  in  accordance  with  the  ever- 
changing  conditions.  With  the  assistance  of  the  drawings,  which 
were  so  selected  as  to  cover  all  the  more  important  points,  and 
which,  taken  as  a  whole,  constitute  a  very  complete  and  easily  un- 
derstood history  of  the  tunnel,  it  is  hoped  that  the  character  of 
the  difficulties  may  be  appreciated  and  the  methods  by  which  they 
were  overcome  fully  comprehended. 

The  writer's  opportunities  for  close  and  careful  inspection  have 
been  most  favorable  from  almost  the  beginning  of  the  enterprise. 
It  has  been  his  duty,  while  attached  to  technical  journals  of  this 
city,  to  examine  and  describe  the  operations  at  the  tunnel.  Visits 
were  frequent,  and  the  purpose  was  early  formed  of  some  day 
collecting  and  arranging  the  data  obtained.  The  larger  part  of 
the  articles  then  written  appeared  in  Engineering  News,  and  Avere 
made  up  of  notes  almost  invariably  personally  obtained  in  the 
heading  of  the  tunnel. 

The  writer  wishes  to  acknowledge  the  kind  courtesy  of  Mr.  D. 
C.  Haskin,  manager  of  the  company,  who  loaned  the  note-books 
and  working-drawings  of  his  office. 

S.  D.  V.  B. 

New  York,  January,  1885. 


CONTENTS. 


CHAPTER  I.  paob 

Necessity  for  a  tunnel — Hudson  Tunnel  Railroad  Company — Location, 

length,  and  grade  of  tunnel 9 

CHAPTER  II. 

Method  of  building — Compressed  air — Form  and  dimensions,  and  sink- 
ing, of  shaft — Air-lock  in  shaft— Effect  of  air-pressure  upon  silt — 
Temporary  entrance  .........     13 

CHAPTER  III. 

Starting  tunnels — Method  of  building — Disposition  of  excavated  ma- 
terial— Bold  plan  adopted  in  beginning  south  tunnel — Difficulties 
caused  by  old  crib  bulkhead — Removing  temporary  entrance — Ac- 
cident— Condition  of  work  at  time  of  accident  .         .         .         .20 

CHAPTER  IV. 

Plans  for  recovering  the  bodies  and  opening  the  work — Open  cut,  coffer- 
dam, caisson — Description  of  coffer-dam  and  caisson — Air-locks  in 
caisson — Sinking  caisson — Opening  old  air-lock — Forcing  silt  into 
south  tunnel 26 

CHAPTER  V. 

Resuming  work — Illumination — Condition  of  atmosphere — Air-compres- 
sors— Steam  supply — Telephone — Supplying  material — Removing 
excavated  material 33 

CHAPTER  VI. 

Shape,  dimensions,  and  use  of  pilot — Advancing  heading — Objects  of 
iron  sheathing — Masonry — Leaks — Bulkheads  in  tunnels — Connect- 
ing working-chamber  with  shaft — Perfected  method  of  obtaining 
supplies  and  removing  silt — Suspension  of  work  on  New  Jersey  side.     39 


('  CONTENTS. 

CHAPTER  VII. 

Silt,  analysis  and  physical  properties — Its  resistance  to  displacement — 
Effect  of  compressed  air  upon  silt — Dry,  moist,  and  saturated  silt — 
The  use  of  compressed  air — Stopping  leaks — Effect  of  compressed 
air  upon  men  and  sensations  in  passing  through  the  air-  lock    .        .    49 

CHAPTER  VIII. 

Plans  for  reaching  grade  of  tunnels  at  New  York  side — Shaft  or  caisson 
— Description  of  caisson — Air-locks — Its  location — Method  of  Sink- 
ing— Plans  for  starting  tunnels — Cutting  through  side  of  caisson — 
Iron  bulkhead — Sizes  of  plates — Method  of  building  the  tunnel — 
Bulkhead  in  tunnel — Handling  material — Sand-pump— Blow-out — 
Piles  met — Work  stopped — Boilers  and  air  compressors — Material 
required  to  complete  tunnels 55 


LIST    OF   ILLUSTRATIONS. 


I.  Map  showing  location  of  tunnel. 
II.  Profile  and  plan  of  tunnel. 

III.  Cross-section  through   temporary  entrance,  looking   toward   shaft 

from  tunnel. 

IV.  (1)   Longitudinal  section  through  temporary  entrance.      (2)  Plan, 

shaft,  temporary  entrance,  and  tunnels. 
V.  Perspective  view  showing  condition  of  temporary  entrance  at  time 

of  accident. 
VI.  Longitudinal  section  through  shaft  and  tunnel  showing  method  of 
working. 
VII.  Coffer-dam  showing  caisson  as  suspended. 
VIII.  Caisson — New  Jersey  side. 
IX.  Vertical  air-lock  in  caisson  :  (1)  Section  and  elevation ;  (2)  front 

view  ;  (3)  section   through  door  and  hinge  ;  (4)  inside  view. 
X.  Longitudinal  section  through  shaft,  caisson,  and  tunnel  after  com- 
pletion of  working-chamber. 
XL  Cross-sections  through  working-chamber  and  completed  tunnels. 
XII.  Side  and  end  view  of  dirt-car. 

XIII.  Plan  and  side  view  of  dump-car. 

XIV.  Longitudinal  and  cross  section  through  pilot. 

XV.  Longitudinal  and  cross  section  through  bulkhead  in  tunnel — New 
Jersey  side. 
XVI.  Horizontal  air-lock  made  in  sections  to  facilitate  moving  to  front : 

(1)  cross-section  at  end  ;  (2)  side  elevation — ends  in  section. 
XVII.   Longitudinal  section  and  plan  showing  tunnels  as  connected  with 

the  shaft. 
XVIII.  (1)  Cross-section  tunnel — Xew  York  side  ;  (2)  cross-section  tunnel 
— Xew  Jersey  side. 
XIX.  Views  of  caisson — New  York  side  :  (1)  Longitudinal  sectional  ele- 
vation ;  (2)  transverse  section  ;  (3)  half  plan. 


8  LIST   OF   ILLUSTRATIONS. 

XX.  Sectional  elevation  through  caisson  and  tunnel — New  York  side. 
XXI.  Cross-section  and  plan  showing  piles  met — New  York  side. 
XXII.  Showing  method  of  building  tunnel  through  sand — New  York  side: 
(1)  cross  and  longitudinal  sections — plates  in  upper  portion  of 
section  ;  (2)  Plates  in  half  of  section  ;  (3)  Section  sheathed  and 
ready  for  masonry. 

XXIII.  End  elevation  of  iron  bulkhead. 

XXIV.  Showing  projection  of  rings  of  plates — working  in  sand. 
XXV.  Sizes  of  iron  plates — New  York  side. 

XXVI.  Longitudinal  section,  plan,  and  cross-section  through  bulkhead — 

New  York  side. 
XXVII.  Longitudinal  section  through  tunnel — New  York  side. 


TUNNELING    . 


I'XDER   TOE 


Hudson     River 


CHAPTER  I. 


NECESSITY   FOR  A  TUNNEL — HUDSON   TUNNEL   RAILROAD   COMPANY — 
LOCATION,    LENGTH,    AND    GRADE   OF  TUNNEL. 

The  Iluclson  River,  flowing  between  New  York  City  and  Jersey 
City,  where  seven  great  railroads  carrying  the  bulk  of  freight  from 
the  West  have  their  termini,  has  always  most  effectually  delayed 
transportation,  and  rendered  impossible  the  sure,  and  at  the  same 
time  the  quick,  delivery  of  freight.  The  magnitude  of  the  bar- 
rier thus  presented  may  be  conceived  when  we  remember  that 
New  York  City  is  not  only  the  largest  shipping  port  in  the  coun- 
try, but  is  also  the  distributing  point  for  freight  between  the  South 
and  West  and  the  East,  and  from  the  East  to  centres  West  and 
South.  We  therefore  find  that  the  few  hours  lost  in  crossing  the 
Hudson  affect  not  only  this  immediate  vicinity,  but  they  also  af- 
fect in  a  much  more  marked  degree  every  point  having  business 
relations  with  New  York,  or  through  New  York  to  points  beyond. 

The  passenger  side  of  this  question  is,  perhaps,  the  more  im- 
portant, although  the  reduction  by  the  use  of  a  tunnel  would 
amount  to  an  average  of  but  a  few  minutes  ;  but  these  short  pe- 
riods consumed  by  ferriage  become  worthy  of  most  careful  consid- 
eration in  this  age  of  quick  travel  and  obstinate  competition. 

There  are  but  two  plans  of  obviating  this  difficulty — building  a 

9 


10  TUNNELING   UNDEK  THE   HUDSON   EIVER. 

bridge  or  a  tunnel.  The  tremendous  cost  of  the  first,  arising  from 
many  causes  which  will  appear  to  the  observer,  places  it  out  of  the 
question.  Projects  for  tunneling  under  this  stream,  which  has  a 
swift  tidal  current  and  a  deep  channel,  have  long  been  discussed, 
but  by  all  of  the  old  and  established  methods  of  submarine  tunnel- 
ing the  cost  has  stood  in  the  way,  for  the  simple  reason  that,  if 
built  with  private  capital,  the  charges  or  toll  would  have  to  be  so 
large,  in  order  to  pay  an  interest  on  the  amount  invested,  as  to 
make  its  use  practically  impossible.  The  benefit  to  be  derived  was 
not  commensurate  with  the  expenditure  when  it  could  only  be  ob- 
tained at  the  rate  of  a  few  inches  per  day  ;  consequently  it  became 
evident  that  some  cheaper  plan  must  be  brought  forward  before  a 
roadway  could  be  built  under  the  river.  That  some  of  the  estab- 
lished plans  were  perfectly  feasible  is  most  probable,  and  that  they 
could  only  be  prosecuted  slowly  and  at  excessive  cost  is  most  cer- 
tain. The  great  size  of  the  tunnel  was  no  mean  obstacle,  for,  in 
order  to  accommodate  travel,  it  would  have  to  be,  if  single,  huge 
enough  for  two  tracks,  since  a  single-track  tunnel  would  not  clear 
away  the  obstructions  to  transportation,  and  would  cost  much  more 
than  one-half  the  sum  which  one  carrying  a  double  track  would. 
The  question  then  resolved  itself  into  one  double-track  single  tun- 
nel or  two  single-track  parallel  tunnels. 

For  the  purpose  of  constructing  a  railroad  through  a  tunnel 
under  the  Hudson  between  t lie  two  cities  the  Hudson  Tunnel  Rail- 
road Company  was  organized,  with  a  capital  of  $10,000,000,  under 
the  general  railroad  laws  of  New  York  and  New  Jersey.  This  cor- 
poration is  independent  of  the  railroads  now  existing,  and  was  de- 
pendent solely  upon  its  own  financial  ability  to  carry  out  the  work 
it  proposed. 

In  locating  the  Hudson  River  Tunnel  three  questions  came 
prominently  up  for  consideration.  The  various  routes,  upon  any 
one  of  which  the  tunnel  could  have  been  begun,  while  differing 
essentially  from  each  other  in  some  points  of  minor  importance, 
yet  presented  the  same  general  features  regarding  the  material  to 
be  passed  through  and  the  engineering  difficulties  to  be  surmounted. 
The  river  at  this  locality  varies  but  little  in  width  or  depth,  being 
a  trifle  over  a  mile  across  and  sixty  feet  deep  in  the  channel,  and 
the  shores  and  bottom  do  not  change  much  either  in  composition  or 


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TUNNELING   UNDER  THE   HUDSON   RIVER.  11 

contour  between  the  extreme  points  at  which  the  tunnel  might  hare 
been  located.  The  bed  of  the  river  consists  of  silt,  which  extends 
from  the  New  Jersey  or  western  side  nearly  or  quit*'  across  the 
river ;  upon  the  New  York  side,  near  the  shore,  some  rock  is  en- 
countered, between  which  and  the  shore  sand  underlies  the  silt. 

Owing  to  this  peculiarity  of  formation  the  tunnel  would  be 
embedded  for  nearly  its  whole  length  in  silt,  no  matter  where  its 
location  might  be  ;  and,  governed  by  these  circumstances,  the  esti- 
mated cost  of  the  work  in  each  of  the  locations  did  not  change  much 
when  confined  to  the  tunnel  proper.  The  approaches,"  of  course,  va- 
ried considerably  with  each  location,  and  the  selection  depended 
directly  upon  the  value  of  the  land  to  be  acquired  at  each  terminus, 
thereby  influencing  the  total  cost  of  the  work  as  a  whole. 

But  the  final  and  paramount  question,  upon  which  the  real  suc- 
cess of  the  scheme  depended,  was  what  might  be  termed  the  ac- 
cessibility of  each  end,  or,  in  other  words,  the  convenience  of  using 
the  stations  and  their  adaptability  to  the  requirements  of  trade. 
Upon  the  New  York  side  this  was  governed  primarily  by  the  fact 
that  it  should  be  so  situated  as  to  be  easily  reached  from  the  centre 
of  the  city,  and  yet  the  site  should  not  be  in  a  neighborhood  in 
which  the  land  damages  would  be  so  great  as  to  be  in  reality  pro- 
hibitory. Upon  the  other  side  of  the  river  it  had  to  be  so  located 
that  the  great  railroads  having  their  termini  there  could  acquire 
access  to  it  at  a  minimum  cost. 

After  a  careful  examination  of  all  the  questions  involved,  the 
tunnel  was  finally  located  on  a  line  extending  easterly  from  Jersey 
Avenue  (Jersey  City),  on  Fifteenth  Street,  to  Hudson  Street,  about 
3,400  feet ;  from  this  point  it  curves  five  degrees  northward  to  the 
New  York  City  bulkhead  line  at  the  foot  of  Morton  Street,  about 
5,500  feet,  and  thence  again  slightly  southward  about  4,000  feet  to 
the  eastern  station.  As  will  be  seen  by  consulting  the  accompanying 
map,  this  line  places  the  eastern  end  in  one  of  the  best  locations  in 
the  city,  and  also  furnishes  the  most  convenient  point  upon  which 
to  concentrate  the  various  railroad  lines  upon  the  New  Jersey  side 
with  the  least  possible  injmy  to  existing  interests.  More  than  this, 
the  line  encounters  as  little,  if  not  less,  rock — which  never  comes 
nearer  than  28  feet  from  the  bottom  of  the  river,  and  is  wholly 
confined  to  a  small  knoll  near  the  eastern  shore — than  any  other, 


12  TUNNELING   UNDER  THE  HUDSON    RIVER. 

and  insures  plenty  of  head-room  in  silt.  The  composition  of  the 
material  encountered  along  the  entire  line  is  shown  very  clearly  in 
the  plan  and  profile  (Plate  II.) 

This  plate  also  shows  the  grade  of  the  tunnel.  The  slope  from 
the  western  end  is  two  feet  in  a  hundred  to  a  point  about  1,600 
feet  from  the  shore,  where  the  slope  changes  to  one  foot  in  one  hun- 
dred ;  this  continues  to  within  1,300  feet  of  the  eastern  shore, 
where,  for  a  distance  of  300  feet,  it  is  one  foot  in  one  hundred. 
For  500  feet  the  grade  is  four  in  one  hundred,  and  for  2,000  feet 
the  grade  is  three  feet  in  one  hundred;  thence  to  station  the  grade 
is  moderate,  conforming  with  the  surface.  The  grade  accords  very 
nearly  with  the  slope  of  the  river-bed,  and  became  necessary  from 
the  fact  that  it  was  decided  that  at  no  point  should  the  crown  of 
the  arch  approach  nearer  to  the  water  than  15  feet.  This  was  to 
insure  safety  in  the  work  and  to  guard  against  any  change  which 
might  take  place  in  the  future  in  the  bed  of  the  river. 


Plate    II. 


BO  120  160 

I  I  I        VERTICAL  SCALE 

PROFILE  AND  PLAN  OF  TUNNEL. 


PLAN  OF  TUNNEL.  SHOWING  DISTANCE  FINISHED  ON  N.Y.SIDE. 


CHAPTER  II. 

METHOD  OF  BUILDING — COMPRESSED  AIR— POEM  AND  DIMENSIONS, 
AND  SINKING,  OF  SHAFT — AIR-LOCK  TN  SHAFT — EFFECT  OF  AIR- 
PRESSURE    DPON   SILT — TEMPOEAET    ENTRANCE. 

The  plan  or  method  of  carrying  the  work  forward  was  by  the 
use  of  compressed  air,  as  applied  in  patents  granted  to  Mr.  D. 
C.  Haskin,  the  president  and  manager  of  the  company.  This  plan, 
briefly  stated— for  we  shall  describe  its  exact  operation  in  detail 
further  on — consisted  in  maintaining  an  air-pressure  in  the  work 
about  equal  to  the  hydrostatic  head.  It  was  well  known  that  if 
these  two  elements — the  air-pressure  inside  and  the  water-pres- 
sure outside — could  be  so  controlled  as  to  maintain  a  constant  and 
unchanging  equilibrium,  the  material  separating  them  need  not  be 
either  of  great  size  or  strength.  It  was  calculated  that  the  silt, 
when  in  proper  condition,  would  have  tenacity  or  consistency 
enough  to  answer  this  object ;  and  although  it  was  known  that 
this  would  only  serve  the  purpose  for  a  brief  time — the  exact 
duration  could  in  no  way  be  experimentally  determined — it  was 
thought  that  there  would  be  ample  time  to  place  and  secure 
the  iron  plates  forming  the  exterior  of  the  tunnel.  It  was  known 
that,  with  the  plates  once  in  position  and  bolted  together,  the 
interior  air-pressure  would  take  the  place  of  struts  to  keep  them 
in  position — a  feature  which  would  not  only  relieve  the  working 
space  of  encumbrance,  but  would  give  a  much  better  support  for 
the  plates  while  the  masonry  was  being  put  in.  A  plate  30  by 
50  inches  would  be  subjected,  at  a  depth  of  4o  feet,  to  a  pres- 
sure of  30,000  pounds.  At  a  normal  interior  pressure  this  plate 
would  have  to  be  supported  at  several  points  in  order  to  prevent 
bending,  or,  in  case  a  single  strut  were  employed,  it  would  have  to 
be  made  of  great  thickness  and  the  strut  would  be  of  a  size  so 
large  as  to  most  seriously  occupy  the  space.  But  with  the  use  of 
compressed  air  at  20  pounds  pressure  per  inch  the  plate  would  be 
supported  at  every  point  and  its  thickness  would  become  a  question 
of  minor  importance.    It  is  hardly  necessary  to  state  that  these 

13 


14  TUNNELING  UNDER  THE   HUDSON   RIVER. 

things  were  all  carefully  considered  before  the  work  was  begun. 
How  well  compressed  air  alone  answered  the  purpose  will  be  found 
as  we  advance  with  the  undertaking. 

After  a  year  spent  in  taking  soundings  and  boring  on  the  line 
adopted,  work  on  the  tunnel  was  begun  in  November,  1874,  it  hav- 
ing been  decided  to  sink  a  shaft  on  the  New  Jersey  side  near  the 
river  line,  and  from  the  side  of  the  shaft  start  the  tunnel.  The  po- 
sition of  the  shaft  in  relation  to  the  tunnels  is  clearly  indicated  in 
the  plan-view  in  Plate  IV.,  and  its  position  on  the  shore,  83  feet  from 
the  bulkhead- wall,  is  shown  in  Plate  VI.  It  is  circular  in  form, 
having  an  inside  diameter  of  30  feet,  an  outside  diameter  of  38  feet, 
the  thickness  of  the  wall  at  the  bottom  being  4  feet  and  at  the  top 
2%  feet ;  the  batter  of  the  outer  surface  is  one  inch  in  three  feet,  or 
a  total  of  20  inches.  It  was  sunk  to  a  depth  of  60  feet  below  the 
ground-surface,  passing  first  through  9  feet  of  loose  ash-filling,  then 
50  feet  of  silt,  the  bottom  finally  resting  in  sand.  A  shoe  was  first 
built  in  an  excavation  a  few  feet  deep,  and  upon  this  the  masonry 
(brick)  was  laid,  the  mass  sinking  as  material  was  removed  from 
under  the  shoe. 

The  shoe  was  made  of  10  by  12-inch  yellow  pine,  held  together 
in  ship-work  style  by  drift-bolts.  It  had  a  cutting  edge  of  boiler- 
iron,  and  was  4  feet  high  by  4  feet  wide  at  the  top,  the  section  being 
triangular.  Upon  each  of  the  east  and  west  sides  of  the  shaft  there 
was  built  a  false  piece  24  feet  high  by  26  feet  wide,  having  an  ellip- 
tical form,  and  which  was  to  be  finally  removed  to  make  room  for 
the  approach  and  the  tunnel.  These  sections  were  laid  in  common 
mortar — the  rest  of  the  shaft  being  laid  in  Rosendale  cement — and 
during  the  sinking  caused  considerable  trouble,  as  the  false  work 
in  the  river-side  was  forced  in,  by  the  pressure  of  the  earth,  to  such 
an  extent  as  to  require  interior  bracing.  The  projection  at  the  top 
amounted  to  7  inches,  decreasing  to  nothing  at  the  bottom.  The 
bracing  consisted  of  heavy  yellow-pine  timbers  formed  into  a  hex- 
agonal collar-brace  ;  four  sets,  at  varying  heights,  were  put  in,  and, 
while  they  served  the  purpose  admirably,  they  also  acted  as  sup- 
ports for  the  platforms  afterward  required. 

Sinking  of  the  shaft  continued  until  December  15,  1874,  when, 
after  thirty  days'  work,  the  shoe  was  14  feet  below  mean  high  water, 
when  work  was  stopped  by  an  injunction  obtained  by  the  Delaware, 


TUNNELING    UNDER   THE    HUDSON    KIVKK.  15 

Lackawanna  &  Western  Railroad  Company.  On  account  of  litiga- 
tion work  was  not  resumed  until  September,  1879. 

Material  was  taken  out  by  a  hoisting-engine,  the  vibrations  of 
which  caused  that  part  of  the  shaft  nearest  to  it  to  sink  faster  than 
the  remaining  portions  ;  and  to  overcome  this  difficulty  the  engine 
was  moved  about,  when  the  settlement  could  be  better  controlled. 
On  November  3  the  shaft  was  in  position,  with  the  shoe  54  feet  be- 
low mean  high  water,  or  GO  feet  from  the  surface  ;  the  average  rate 
of  progress  was  one  foot  per  day.  During  the  sinking  no  difficulty 
was  experienced  in  keeping  the  shaft  free  of  water  by  the  aid  of 
an  ordinary  hand-pump  ;  but  as  soon  as  the  shoe  entered  the  sand 
stratum  water  poured  in  at  the  rate  of  about  200  gallons  per  minute. 
While  making  the  excavation  two  pumps  were  used  alternately  to 
keep  the  water  down — an  Andrews  pump  of  300  gallons'  capacity 
per  minute,  and  a  Pulsometer  of  100  gallons'  capacity. 

This  movement  displaced  all  the  earth  immediately  adjacent  to 
the  shaft.  The  silt  moved  down  the  outside  and  under  the  shoe, 
and  was  followed  by  the  ash-filling,  the  approximate  positions,  as 
determined  later  on,  being  indicated  in  Plates  Y.  and  YI.  The 
appearance  of  the  ashes,  low  down  on  the  side  of  the  shaft,  was 
the  direct  cause  of  much  trouble  later  on  when  the  work  was 
being  prosecuted  in  this  locality,  since  the  ash  mixing  with  the  silt 
injured  the  hitter's  tenacity  and  made  its  behavior  under  air-pres- 
sure uncertain.  The  displacement  w^as  also  aided  by  the  sinking  of 
the  shaft  itself,  since,  as  it  descended,  the  friction  of  its  outer  sur- 
face tended  to  dislodge  the  material  and  subsequently  made  the 
passage  of  the  water  down  the  side  much  easier.  Building  project- 
ing courses  about  the  shaft  would  not,  in  all  probability,  have  ob- 
viated the  difficulty  ;  and  if  the  work  had  been  arrested  for  a  time 
just  before  the  shoe  entered  the  sand  stratum  the  water  would  not 
have  been  finally  excluded  from  the  bottom.  If  the  latter  course 
had  been  pursued  it  is  doubtful  if  the  shaft  could  have  been  started 
again  on  its  course,  so  great  is  the  clinging  power  of  the  silt  when  it 
has  been  allowed  a  little  time  to  settle  around  an  object.  Piles  driven 
along  this  shore  move  down  easily  when  quickly  driven,  and  when 
driven  too  far  may  be  pulled  up,  no  settlement  taking  place  after 
the  silt  has  had  time  to  accommodate  itself  to  the  new  conditions. 

In  order  to  lay  the  concrete  bottom  the  water  was  confined  as 


16  TUNNELING   UNDER  THE   HUDSON    RIVER. 

much  as  possible  in  covered  chambers,  a  number  of  4-inch  iron 
pipes  being  laid  (radiating)  from  a  well  having  an  open-slat  wooden 
curb  4^  feet  across  at  the  bottom,  2  feet  at  the  top,  and  4  feet  in 
height ;  this  was  lined  with  loose  brick  and  placed  at  its  full  depth 
in  a  convenient  situation  in  the  bottom.  That  portion  of  the  bot- 
tom least  exposed  to  water  was  first  covered  with  a  foundation  of 
securely -embedded  dry  stone  from  12  to  18  inches  deep,  and  then 
concrete  was  put  on  in  layers  from  8  to  12  inches  deep.  An  adjoin- 
ing section  was  then  treated  in  the  same  way  until  the  entire  bottom 
had  been  put  in  and  the  water  confined  to  the  well-hole.  The  ave- 
rage thickness  of  the  concrete  was  2%  feet — that  at  the  centre  being 
2l/2  feet  and  the  sides  varying  from  3  to  3-^  feet.  The  concrete  was 
mixed  as  follows  :  One  cement,  two  sand,  two  stone,  and  one  gravel. 
Water,  carrying  sand  with  it,  still  came  through  the  well,  the  filling 
of  which  with  dry  stone  only  stopped  the  sand  to  a  small  extent. 
Consequently,  a  12-inch  stand-pipe  was  carried  up  from  the  well  for 
a  distance  of  25  feet,  at  which  point  a  reducer  was  put  on  and  a 
4-inch  length  extended  to  above  high-water  level.  The  water  in  this 
pipe  rose  and  fell  with  the  tide,  but  not  in  the  same  proportion,  nor 
did  the  level  reach  that  of  the  river.  The  well-hole  about  the  pipe 
was  at  last  filled  with  concrete,  which  was  mixed  in  bags  and  placed 
in  the  hole,  which  had  been  previously  cleaned  out  and  the  sides 
dug  away  so  as  to  form  a  cone.  Other  attempts  to  concrete  this 
portion  had  been  unsuccessful,  as  the  water-pressure  was  sufficient 
to  wash  out  the  concrete  :is  fasl  as  it  was  put  in  ;  but  by  using  bags 
the  concrete  was  held  until  it  had  time  to  set,  the  outwardly  and 
downwardly  sloping  sides  preventing  any  dislodgment. 

The  air-lock  (Plate  IV.)  was  a  cylindrical  tube  of  ^-inch  boiler- 
iron,  built  up  of  plates  3  feet  wide  and  extending  hall- way  round. 
Although  it  was  15  feet  long  by  0  feet  in  diameter,  it  proved  to  be 
admirably  adapted  for  convenient  use.  In  each  end  there  was 
a  door  3  feet  wide  by  4  feet  high,  and  so  hung  upon  strap-hinges 
3  inches  wide  by  ^  inch  thick,  placed  10  inches  above  the  bottom 
and  the  same  below  the  top,  and  extending  across  the  door,  that  it 
swung  inward  or  toward  the  air-pressure.  The  door-frame  was  of 
4-inch  angle-iron,  riveted  to  the  head,  Which  was  stayed  by  live 
2-inch  braces  that  were  2  feet  long  and  were  riveted  to  the  shell.  The 
door  was  further  strengthened  by  two  strips  of  4-inch  T-h'on  placed 


TUNNELING   UNDER  T1IK    HUDSON  RIVEB.  17 

horizontally.  The  doors  and  heads  were  each  ]/2  an  inch  thick. 
There  was  a  bull's-eye  in  each  door  and  one  in  each  head  beside  the 
door,  made  of  1-inch  thick  glass  9  inches  in  diameter,  the  exposed 
portion  being  7^  inches  across.  Extending  entirely  through  the 
air-lock  were  thirteen  pipes  varying  from  1  to  4  inches  in  diameter 
and  used. for  air  and  water  supply,  electricdight  and  telephone 
wires,  blow-out  pipes,  etc.  There  was  also  a  6-inch  pipe  leading 
through  the  inner  end  of  the  air-lock  and  passing  through  the  side 
of  the  lock  to  the  bottom  of  the  shaft.  There  was  also  a  collar  of 
angle-iron  6  inches  wide  and  }4  an  inch  thick,  securely  fastened 
around  the  outside,  against  which  to  brace  to  secure  the  lock  in 
position.  The  air-lock  was  used  for  the  passage  of  men  and  ma- 
terials, and  was  supposed  to  be  the  largest  one  ever  built. 

In  the  side  of  the  shaft,  at  the  top  of  the  false  piece  previously 
mentioned,  29  feet  below  top  of  shaft,  an  opening  was  made  to 
receive  the  air-lock.  (In  order  to  show  the  nature  of  this  silt  it 
may  be  well  to  state  here  that  it  gradually  and  regnlarly  pushed  its 
way  through  a  small  opening  which  had  been  made  in  the  shaft, 
keeping  the  form  of  the  hole  until  it  projected  a  little  way  from 
the  wall,  when  its  own  weight  broke  it  off  and  it  fell  to  the  bot- 
tom, but  still  retained  its  shape.)  This  opening  was  not  carried 
completely  through  the  masonry,  a  thin  shell  of  brick  being  left 
upon  the  inner  side.  The  air-lock  was  then  lowered  down  the  shaft 
until  it  was  opposite  the  opening,  when,  by  means  of  hydraulic  jacks 
braced  against  the  opposite  wall,  it  was  forced  through  until  it  pro- 
jected 4  inches  beyond  the  outside  of  the  shaft.  Then  the  brick 
wall  was  fitted  around  t-he  air-lock,  being  strengthened  by  a  collar  of 
yellow-pine  timber,  and  securely  braced  from  the  opposite  side  of 
the  shaft  so  as  to  prevent  any  change  of  position  upon  the  air-pres- 
sure being  put  on  from  the  front. 

To  remove  the  temporary  door  of  boards  which  had  been  se- 
cured to  the  forward  end  of  the  lock,  and  which  was  held  by  the 
pressure  of  the  earth  against  it,  and  begin  the  tunnel  work  was  the 
next  operation  in  order — one  which  was  watched  with  absorbing  in- 
terest, since  the  time  had  come  to  practically  test  the  adaptability  of 
silt  for  the  work,  as  illustrated  by  its  air-resisting  properties.  Men 
entered  the  lock,  closed  the  rear  door  behind  them,  and  after  an  air- 
pressure  of  12  pounds  to  the  square  inch  had  been  put  on  they  re- 


18  TUNNELING   UNDER  THE   HUDSON   RIVER. 

moved  the  temporary  door,  when  the  silt  was  cleared  slowly  away 
until  the  iron  door  could  be  put  in  place  and  swung  wide  open.  It 
was  soon  found  that  silt,  when  of  the  proper  degree  of  moisture, 
was  impervious  to  air,  and  the  great  problem,  that  the  silt  would  hold, 
the  air  and  the  air  would  hold,  the  silt,  was  practically  solved.  At 
this  time  it  was  the  intention  to  build  a  double- track  single  tunnel, 
24  feet  high  by  20  feet  wide  in  the  clear,  and  the  excavation  was  ex- 
tended partly  around  the  shaft,  and  on  January  2,  1880,  the  chamber 
dug  was  0  feet  high,  15  feet  wide,  and  4  feet  deep.  No  attempt  was 
made  to  protect  the  silt  from  the  air,  which  gradually  forced  back 
the  water,  minute  holes  iirst  indicating  an  excessive  dryness  ;  these 
holes  increased  in  size  and  developed  into  cracks,  which  extended 
up  through  the  silt,  in  about  four  days,  to  the  loose  ash-filling 
that  had  been  carried  down  by  the  shaft,  as  already  mentioned,  and 
through  which  the  water  flowed  as  they  increased  in  size.  Before 
the  water  found  a  passage  the  roof  began  to  fall;  Iirst  small,  then 
large  pieces  of  dry  silt  would  become  detached  and  drop.  The  top 
was  kepi  in  place  four  days  by  the  air-pressure,  but  as  the  water 
had  a  disintegrating  effect  upon  the  silt,  which  seemed  to  mix  with, 
and  be  held  in  suspension  by.  it,  the  excavation  was  refilled  soon 
after  the  cracks  appeared,  the  men  retiring  into  the  air-lock  and 
closing  the  door. 

A  hole  was  now  dug  at  the  surface  immediately  above  the  inner 
end  of  the  lock,  30  feet  wide,  9  feet  below  high  water,  and  extend- 
ing 20  feet  from  the  side  of  the  shaft  toward  the  river.  Carefully 
spread  over  the  bottom  of  this  hole,  and  carried  a  short  way  up 
on  the  shaft,  was  a  canvas,  held  down  by  heavy  timbers,  upon 
which  the  excavated  material  was  replaced.  This  expedient  was 
adopted  in  order  to  in-even t  the  entrance  of  water  into  the  work 
next  to  the  shaft.  While  this  work  was  being  performed  the  plates 
for  a  temporary  entrance  leading  to  the  inner  lock-door  had  been 
made.  This  entrance  (Plate  IV.)  was  a  tube  8  feet  long  by  0.^  feet 
in  diameter,  composed  of  plates  2}/2  by  4  feet,  with  3-inch  angle- 
irons  riveted  along  each  edge.  This  tube  lapped  over  the  projecting 
part  of  the  air  lock,  to  which  it  was  secured,  and  was  made  of  iron 
y2  an  inch  thick  ;  this  amount  of  strength  being  considered  requi- 
site, since  the  tube  was  designed  to  prevent  the  air-lock  door  from 
ever  becoming  wedged  should  a  caving  of  the  roof  take  place. 


Plate 


CROSS  SECTION   THROUGH  TEMPORARY  ENTRANCE 
LOOKING  TOWARD  SHAFT  FROM   TUNNEL. 


Plate  V. 


PERSPECTIVE  VIEW  SHOWING  CONDITION  OF  TEMPORARY  ENTRANCE  AT  TIME  OF  ACCIDENT. 


Plate  IV. 


SAND 


LONGITUDINAL  SECTION  THROUGH  TEMPORARY  ENTRANCE. 


PLAN  SHAFT,  TEMPORARY  ENTRANCE  AND  TUNNE 


n 


Kiq 


. 


. 


TUNNELING    tTNDEH   THE    BUDSON    RIVER.  19 

From  the  (Mid  of  the  temporary  entrance  there  was  built  a  series 
of  iron  rings— to  gel  away  from  the  shaft  into  undisturbed  silt — 
(Plates  III.,  IV.,  and  V.),  each  being  2  Eeel  wide,  ;:,  of  an  inch 
thick,  and  each  being  18  Inches  larger  than  the  one  just  preceding 
it.  These  rings  were  secured  together  at  the  top,  which  sloped 
so  as  to  meet  the  proposed  grade  of  the  tunnel.  The  angular 
spaces  formed  by  the  lower  portions  of  the  rings  were  filled  tem- 
porarily with  concrete.  The  diameter  of  the  largesl  ring  was  20 
feet.  To  place  the  plates  forming  these  rings  in  position  an  excava- 
tion was  made  in  the  top  adjoining  the  plate  already  in,  when  the 
centre  upper  plate  of  the  next  ring  was  put  up  and  bolted  to  the 
finished  work.  Then  an  excavation  was  made  at  each  end  of  this 
plate,  to  which  the  second  and  third  plates  were  joined.  As  the  cir- 
cles were  eccentric  to  each  other,  touching  only  at  the  top,  the 
centre  plates  could  only  be  held  together  by  two  or  three  bolts. 
The  air-pressure  was  increased  as  the  work  advanced,  and  thus  early 
it  was  learned  that  there  could  be  no  rule  laid  down  by  which  to 
estimate  the  exact  pressure  needed.  The  correct  amount  lluctuated 
considerably,  and  to  a  certain  degree  was  independent  of  the  hydro- 
static head;  the  density  and  composition  of  the  material  directly 
overhead  exerted  a  direct  influence  upon  the  pressure,  which  could 
only  be  determined  by  closely  wa telling  the  behavior  of  the  earth 
under  the  pressure  it  was  at  the  time  exposed  to,  and  change  the 
air  accordingly.  After  the  completion  of  the  eleven  rings  constitut- 
ing the  entrance  the  north  tunnel  was  started,  it  having  been  de- 
cided to  build  two  parallel  single-track  tunnels  instead  of  one 
large  one. 


CHAPTER  III. 

STARTING  TUNNELS — METHOD  OF  BUILDING — DISPOSITION  OF  EXCA- 
VATED MATERIAL — BOLD  PLAN  ADOPTED  IX  BEGINNING  SOUTH 
TUNNEL — DIFFICULTIES  CAUSED  BY  OLD  CRIB  BULKHEAD — RE- 
MOVING TEMPORARY  ENTRANCE— ACCIDENT— CONDITION  OF  WORK 
AT  TIME   OF  ACCIDENT. 

The  starting  of  this  work  was  very  difficult,  requiring  much  care 
and  watchfulness  at  every  step.  The  north  tunnel  was  the  first  one 
begun.  The  entrance,  or  connecting-chamber,  as  it  was  afterward 
more  commonly  called,  being  but  20  feet  in  diameter  at  its  river 
end,  would  only  cover  the  adjoining  walls  and  not  one-half  of 
the  arch  and  invert  of  each  tunnel.  To  build  the  outer  sections 
was,  therefore,  the  hazardous  part  of  the  undertaking.  But  experi- 
ence had  already  shown  that,  having  a.  firm  foundation  to  which  to 
attach  an  iron  plate,  the  work  could  be  readily  carried  on  in  any 
direction  or  form.  A  space  was  excavated  huge  enough  to  permit 
the  insertion  of  a  plate,  which  was  secured  by  holts  to  the  plates  of 
the4ast  ring  which  served  as  a  foundation  to  work  from.  Thus  tie- 
work  was  prosecuted  plate  by  plate  until  an  iron  band,  or  shell, 
of  a  size  equal  to  the  exterior  of  the  tunnel,  was  constructed,  in 
which  the  brick-work  was  laid.  The  vertical  space  between  the 
north  side  of  the  entrance  and  the  outer  side  of  the  north  tunnel  was 
securely  bulkheaded,  the  plan  being  to  build  a  certain  length  of 
each  tunnel,  and  then  return  to  replace  the  temporary  work  by 
uniting  the  tunnels  and  shaft.  The  air-pressure,  about  18  pounds 
to  the  square  inch,  held  the  silt  firmly  in  place  while  the  rings  were 
being  made. 

From  this  time  the  tunnel  was  built  in  the  following  way,  which 
is  very  plainly  shown  in  the  drawing  (Plate  VL)  Silt  was  removed 
until  the  top  centre  plate  could  be  put  in  and  bolted  to  the  one  be- 
hind. Then  a  plate  was  put  in  at  each  side  and  bolted  to  the  centre 
plate  and  to  the  ring.  When  this  circle  had  been  carried  down  the 
sides  for  some  distance  another  was  commenced  and  built  in  the 


LONGITUDINAL  SECTION  THROUGH  SHAFT  AND  TUNNEL  SHOWING  METHOD  OF  WORKING 


TUNNELING    UNDER  THE  HUDSON   RIVER.  21 

same  manner.  When  four  rings  of  plates  had  been  put  up  and 
thoroughly  braced  as  additional  protection  in  case  of  a  reduction  in 
the  air-pressure,  this  iron-lined  chamber  was  cleaned  out  and  the 
masonry  laid,  thus  completing  a  section  of  10  feet.  Both  the  iron- 
work and  masonry  were  advanced  in  sections  varying  from  10  to  -15 
feet  in  length.  During  the  first  few  weeks  the  rate  of  progress  only 
averaged  about  1  foot  per  day,  but  as  the  men  became  more  familiar 
with  the  work,  which  was  soon  put  in  systematic  shape,  the  rate 
increased  to  an  average  of  nearly  5  feet  of  completed  tunnel  every 
24  hours.  The  heading,  which  was  cut  into  steps,  as  indicated  in 
the  drawing,  was  entirely  exposed  to  the  air-pressure,  no  attempt 
whatever  being  made  to  sheathe  any  part  of  it ;  but  all  digging  to 
advance  the  heading  was  done  carefully  and  without  undue  haste, 
since  at  any  moment  a  less  compact  material,  or  "  pocket,"  might  be 
opened.  It  was  the  duty  of  some  of  the  men  to  watch  for  leaks — 
in  the  temporary  work  at  the  entrance — which,  if  of  some  size, 
could  be  detected  by  the  noise  made  by  the  out-rushing  air  ;  when 
small  a  candle  passed  close  to  the  surface  would  show  the  leak  by 
the  flame  being  drawn  in  the  hole  by  the  escaping  air.  The  leaks 
were  easily  controlled  by  the  application  of  fresh  silt. 

About  one-half  of  the  excavated  material — which  was  conveyed 
to  the  air-lock  upon  a  car,  the  track  being  extended  as  the  work 
advanced — was  removed  from  the  tunnel,  the  remainder  being  left  in 
the  finished  work.  The  machinery  and  all  the  operations  connected 
with  the  removal  of  earth  and  the  introduction  of  supplies  will  be 
described  in  detail  further  on.  At  this  time  the  silt  was  removed 
by  b«ing  first  mixed  in  a  trough — shown  to  the  right  in  Plate  VI. 
— with  Avater,  and  then  blown  through  a  6-inch  pipe  by  the  air-pres- 
sure to  the  shaft,  from  which  it  was  hoisted  to  the  surface  and  con- 
veyed to  the  low  land  just  back  of  the  works. 

The  shell  was  made  of  %.  -inch  boiler-iron  cut  into  plates  2£  feet 
wide  and  3  and  6  feet  long.  On  each  of  the  four  sides  was  a  flange 
3  inches  wide  ;  these  flanges  were  pierced  with  holes  at  every  6  in- 
ches, through  which  each  plate  was  bolted  to  the  four  plates  around 
it.  To  give  additional  strength  to  the  cylinder  the  joints  were 
broken.  The  masonry  was  2  feet  thick,  of  hard-burned  brick  laid 
in  cement.  Four  classes  of  men  were  employed  upon  the  work, 
which  was  pushed  forward  night  and  day — miners,  welders,  laborers, 


22  TUNNELING   UNDER  THE  HUDSON   RIVER. 

and  masons.  The  miners  advanced  the  heading,  the  welders  put  up 
and  united  the  plates,  the  laborers  handled  the  diggings,  and  the 
masons  placed  the  brick-work.  The  men  worked  in  shifts  of  8 
hours  each  each  shift  consisting  of  28  men,  who  were  allowed  half 
an  hour's  recess  in  which  to  come  to  the  surface  to  eat  their  meal ; 
but  it  was  so  arranged  that  one-half,  or  14  men,  remained  on  duty 
while  the  others  went  out. 

The  lines  and  grades  of  this  portion  of  the  north  tunnel,  which 
on  July  1,  1880,  had  been  finished  for  a  distance  of  281  feet  from 
the  shaft,  were  not  good,  and  the  shape  was  irregular.  The  reasons 
ascribed  for  this  were  that  the  plates,  which  were  bent  to  a  circular 
form,  were  joined  to  make  elliptical  rings,  that  the  iron  was  too 
light,  and  that  the  plates  were  extended  too  far  beyond  the  brick- 
work. At  one  time  the  plates  on  top  were  over  50  feet  ahead  of  the 
masonry,  the  result  being  an  almost  imperceptible  settlement,  result- 
ing in  distortion.  This  was  remedied  by  increasing  the  air-pressure 
and  by  not  carrying  the  plates  too  far  in  advance  of  the  finished 
work. 

In  order  to  prevent  the  escape  of  air  through  the  pores  of  the 
brick,  ordinary  red  lead  paint  was    tried  with    but   little   sue 
much  better  results  were  obtained  by  a  wash  of  pure  cement  put  on 
in  several  layers. 

The  plan  pursued  in  beginning  the  south  tunnel  was  a  bold  one 
that  proved  to  be  rapid  and  successful  in  execution.  The  plates 
were  inserted  in  small  openings,  as  in  the  case  of  the  north  tunnel, 
but  instead  of  removing  all  the  material  from  the  iron  cylinder  a 
centre  core  of  silt  was  left.  This  core  was  about  5  feet  long  and  a 
little  less  in  size  than  the  inside  of  the  completed  masonry.  The 
men  burrowed  down  each  side  and  under  this  core,  forming  an  an- 
nular chamber  about  3  feet  wide.  As  the  excavation  was  carried 
down  the  plates  were  put  in,  and  were  supported  by  stints  resting 
against  the  core,  a  cross-section  of  this  part  resembling  a  large  wheel 
having  an  immense  hub  of  earth,  short,  thick  spokes,  and  a  thin  iron 
tire  5  feet  in  width.  In  justice  to  Mr.  Anderson,  the  superintendent, 
it  may  be  stated  that  he  asked  no  one  to  venture  under  this  core 
and  put  in  the  masonry  ;  but,  recognizing  the  fact  that  there  was  a 
possibility  of  the  mass  suddenly  settling,  he  went  under  it  himself 
and  laid  the  first  bricks  in  the  invert.     After  this  the  masonry  ring 


TUNNELING    (JNDEB  THE   BUDSON    B1VEB.  23 

was  quickly  completed,  yel  it  was  some  time  before  the  core,  which 
moved  slowly  and  regularly,  had  settled  down.  The  tunnel  was 
thru  pushed  forward  until  the  advance  plates  struck  the  old 
wooden-crib  bulkhead,  when  work  on  both  tunnels  was  stopped, 
and  operations  were  directed  toward  removing  the  temporary 
entrance,  or  connecting-chamber,  as  this  was  too  weak  to  stand  the 
increased  pressure  required  at  the  heading,  and  permanently  unit- 
ing the  shaft  and  tunnels.  At  the  end  of  the  north  tunnel  a  bulk- 
head was  built  of  4  by  6-inch  timbers  laid  horizontally  and  closely 
together  against  the  silt,  with  their  ends  resting  against  the  ends  of 
the  brick-work  ;  behind  these  were  vertical  timbers  of  the  same  size, 
still  back  of  which  was  another  row  of  horizontal  timbers,  the  last 
two  rows  being  3  or  4  feet  apart.  The  whole  was  braced  by  struts 
supported  in  openings  left  in  the  masonry. 

Tunneling  through  the  wood  and  stone  crib,  which  in  some 
places  projected  half  through  the  tunnel,  was  a  difficult  task.  The 
ends  of  the  piles  had  to  be  cut  off  and  the  horizontal  timbers 
removed  so  as  to  clear  the  iron  plates.  It  was  through  this  old 
bulkhead  that  the  water  came  at  the  time  of  the  accident;  it  caused 
a  great  deal  of  trouble  when  recovering  the  bodies  of  the  men  and 
beginning  anew. 

The  first  work  associated  with  the  removal  of  the  connecting-cham- 
ber was  directed  toward  the  last  or  largest  ring.  The  two  plates 
adjoining  the  centre  one  were  taken  down  and  the  silt  dug  out,  so 
that  when  the  plates  were  re-inserted  they  were  on  the  curve  to  be 
formed  for  the  new  work,  the  object  being  to  construct  a  bridle,  as 
it  were,  to  cover  both  tunnels  with  one  span  or  arch  so  as  to  leave  a 
large  chamber,  as  shown  in  Plate  XL  In  this  way  four  rings  were 
removed  and  the  masonry  built  upon,  as  shown  in  Plate  V.  The 
plates  in  the  roof  of  the  remaining  rings  were  then  taken  down, 
their  place  being  supplied  by  the  hood  forming  the  crown  of  the 
new  work.  This  hood  reached  from  the  completed  work  to  the 
shaft,  which  it  joined  3  feet  above  the  air-lock,  and  then  extended 
down  each  side  and  against  the  shaft  as  close  as  it  could  be  well 
fitted,  as  shown  in  the  cross-section  (Plates  III.,  IV.,  and  V.)  This 
roof  was  about  30  feet  in  width  and  was  braced  by  timbers,  as  in- 
dicated in  the  drawings.  The  general  condition  of  the  work  and 
the  arrangement  of  the  machinery  at  this  time  are  shown  in  Plate 


24  TUNNELING  UNDER  THE  HUDSON   RIVER. 

VI. — the  north  tunnel  (not  shown)  had  been  completed  for  nearly 
300  feet  under  the  river. 

At  about  4.30  o'clock  on  the  morning  of  July  21,  1880.  when 
one-half  of  the  men  had  returned  to  their  work  and  the  other  half 
had  started  for  the  air-lock  to  pass  out  for  their  period  of  rest,  a 
leak  occurred,  the  air  escaping  up  along  the  side  of  the  shaft.  The 
leak  was  probably  caused  by  a  plate  not  being  properly  secured 
against  the  shaft ;  but  of  this  there  is  no  definite  knowledge.  As  the 
men  were  standing  near  the  lock-door  talking  as  to  the  best  course 
to  pursue  the  roof  gave  way,  when  the  falling  earth  and  plates  so 
wedged  the  inner  air-lock  door — it  was  found  open  about  8  inches — 
that  all  efforts  of  the  imprisoned  men  to  open  it  were  unavailing. 
The  men  were  thus  divided  :  eight  were  in  the  lock,  six  of  whom 
had  gone  to  stop  the  leak  and  two  of  whom  had  been  out  to  lunch 
and  returned,  and  twenty,  including  the  assistant  superintendent, 
Peter  Woodland,  were  in  the  connecting-chamber  near  the  door. 
When  it  was  found  absolutely  impossible  to  provide  any  means  of 
escape  for  the  twenty  men,  the  glass  bull's-eye  in  the  outer  end  of 
the  lock  was  broken,  and,  the  pressure  being  soon  reduced  to  nor- 
mal, the  door  was  swung  open  and  the  eight  men  escaped.  Upon 
the  outer  door  being  opened  the  water,  coming  from  the  old  crib 
bulkhead,  rushed  through  the  lock  and  in  a  short  time  filled  the 
shaft.  How  long  a  time  elapsed  between  the  discovery  that  the 
leak  was  beyond  all  control  and  the  filling  of  the  lock  with  water 
is  not  known  with  any  degree  of  certainty  ;  it  must  have  been 
several  minutes.  The  lock  was  amply  large  enough  to  have  held  the 
twenty-eight  men.  When  work  had  been  resumed  the  writer  once 
passed  through  the  lock  with  twenty  men,  and  noted  particularly 
that,  with  a  little  crowding,  ten  more  could  have  been  accommo- 
dated. 

There  are  several  points  which  must  be  mentioned  in  order  that 
this  stage  of  the  work  may  be  thoroughly  understood.  The  material 
just  above  the  lock  was  a  mixture  of  silt  and  cinders,  which  had 
several  times  been  disturbed,  and  which,  while  lacking  the  tenacious 
qualities  of  pure  silt,  was  extremely  treacherous.  The  cinder  had 
gradually  worked  down  until  the  dividing-line  between  it  and  the 
silt  began  about  at  the  lock  (this  is  plainly  shown  in  Plate  V.,  the 
letter  A  indicating  the  location  of  the  blow-out),  and  extended 


TUNNELING    UNDBE  THE   HUDSON   IUVER.  25 

upwind  and  away  from  the  shaft  until  it  reached  the  undisturbed 
ground.  Men  were  therefore  appointed  to  watch  for  and  stop  leaks, 
which  could  be  readily  done  with  silt.  The  upper  plates,  forming 
a  pari  of  the  permanent  shell,  were  one-quarter  of  an  incli  thick, 
and  were  Bupportedby  timbers  resting npona  foundation  made  in 
the  silt  floor.  The  hood  thus  formed  had  a  large  area  for  work  of 
this  kind  ;  the  surface  was  much  too  great  to  be  carefully  guarded, 
especially  when  a  reduction  of  one  or  two  pounds  in  the  air  was  suf- 
ficient to  produce  deflection.  The  edges  of  the  plates  were  not  let 
into  the  masonry  of  the  shaft,  nor  were  they  securely  connected  to 
it.  The  work  had  progressed  so  smoothly,  and  it  being  supposed 
that  all  danger  had  been  passed,  that,  two  or  three  days  before  the 
accident,  several  plates  had  been  removed  from  the  upper  part  of 
the  temporary  entrance,  thereby  leaving  the  door  of  the  lock  unpro- 
tected should  anything  fall  from  above. 

Whether  the  blow-out  first  started  as  a  small  leak  which  was  un- 
perceived  or  neglected  by  the  men  in  their  haste  to  leave  the  tunnel, 
or  whether  it  quickly  developed  into  proportions  placing  it  beyond 
their  power  to  stop,  will  never  be  known.  A  blow-out  in  the  tunnel 
could  only  occur  in  one  of  two  ways  :  first,  by  a  leak  allowing  the 
air  to  escape  through  the  silt ;  second,  by  two  leaks  occurring 
simultaneously.  In  the  first  case  the  air  would  rush  out  until  the 
interior  pressure  had  been  considerably  reduced,  when  the  water, 
taking  the  silt  with  it,  would  flow  in  ;  as  the  air  became  compressed 
it  would  again  overcome  the  weight  of  the  water  and  rush  out. 
These  movements — resembling  the  flow  of  water  from  an  inverted 
bottle — would  be  repeated  until  the  air  had  all  been  displaced,  and 
would,  of  course,  require  more  or  less  time.  But  in  the  second  case 
the  time  necessary  to  effect  the  displacement  would  be  much  short- 
ened, provided  the  conditions  were  such  that  one  opening  would 
permit  the  outward  passage  of  air  while  the  other  admitted  the 
water.  The  features  governing  this  instance  are  so  peculiar  as  to 
render  it  a  most  improbable,  if  not  impossible,  occurrence. 


CHAPTER  IV. 

PLANS  FOR  RECOVERING  THE  BODIES  AND  OPENING  THE  WORK — 
OPEN  CUT,  COFFER-DAM,  CAISSON — DESCRIPTION  OF  COFFER-DAM 
AND  CAISSON — AIR-LOCKS  IN  CAISSON — SINKING  CAISSON — OPEN- 
ING OLD   AIR-LOCK — FORCING   SILT   INTO    SOUTH  TUNNEL. 

To  open  the  work,  so  as  to  recover  the  bodies  of  the  men  and  go 
on  with  the  tunnel,  was  now  the  hard  task.  During  the  day  and  night 
following  the  accident  all  the  pumping  capacity  that  could  be  ob- 
tained was  put  in  operation  and  an  attempt  made  to  pump  out  the 
shaft,  but  with  no  success.  Divers,  sent  down  the  shaft,  found  that 
the  air-lock  was  partly  lilled  with  silt,  but  they  were  unable  to  stop 
the  flow  of  water.  A  few  days  later  it  was  noticed  that  the  water  in 
the  shaft  rose  and  fell  with  the  tide,  clearly  proving  that  there  was  a 
subterranean  connection  between  it  and  the  river.  That  the  water 
was  lowered  in  the  shaft  when  sufficient  pumping  capacity  had  been 
obtained  was  due  to  the  fact  that  it  was  only  fed  through  the  open- 
ings in  the  air-lock,  which  had  been  partially  closed  by  debris  when 
the  water  first  rushed  through. 

The  three  methods  which  seemed  to  give  the  greatest  hopes  of 
success  were  :  By  an  open  cui  ;  by  building  a  roof  within  the  shaft 
and  forcing  the  water  out  by  compressed  air.  and  then  entering  by 
the  old  air  lock  or  by  a  new  one  built  through  the  roof  of  the  tun- 
nel;  and  by  sinking  a  caisson.  Plans  for  a  coffer  dam  were  imme- 
diately prepared,  as  it  would  be  useful,  if  not  essential,  in  either  of 
the  above  methods.  The  reasons  for  this  conclusion  were  that 
no  open  cut  to  the  requisite  depth  of  36  feet  could  be  sunk 
through  that  material  without  such  a  dam  ;  that  a  roof  or  floor 
would  be  dangerous  unless  it  could  be  embedded  in  the  silt  under- 
lying the  loose  filling  which  covered  the  top  of  the  connecting-cham- 
ber ;  and  that,  in  the  event  of  the  caisson  becoming  necessary,  it 
would  be  decidedly  better  to  have  as  much  excavation  as  possible  in 
an  open  cut.  Borings  made  after  the  caving  showed  that  the  loose 
filling   was  about  20  feet  deep,  and,  with  only  the  loose  stone- 


TUNNELING  UNDKK  THE   HUDSON   EIVEE.  27 

crib  bulkhead  along  the  river-front  as  a  protection,  a  deep  excava- 
tion without  the  dam  was  an  impossibility. 

The  coffer-dam  was  therefore  begun.  It  was  46  feet  square 
(Plate  VII.),  and  was  so  built  as  to  embrace  a  portion  of  the  shaft 
which  entered  the  inside  wall  to  a  distance  of  11  feet,  and  also  to  ex- 
tend about  5  feet  east  of  the  west  end  of  the  completed  tunnel.  The 
guide-piles  were  12  inches  square  and  the  sheet-piles  were  6  inches 
thick  by  12  inches  wide.  The  seams  were  calked  to  prevent  the 
entrance  of  water.  The  timbers  were  of  yellow  pine,  and  were  driven 
to  a  depth  of  40  feet,  great  care  being  exercised  in  driving  those 
forming  the  east  wall,  lest  they  should  injure  the  roof  of  the  tunnel. 
Excavation  had  been  carried  on  simultaneously  with  work  on  the 
dam,  and  at  10  feet  below  the  top  a  tier  of  beams  was  placed  in 
position.  As  the  depth  became  greater  water  began  to  interfere  with 
the  work,  and  so  increased  in  volume  that  three  pumps,  throwing 
about  8,000  gallons  per  minute,  could  no  longer  control  it.  A  second 
tier  of  beams  15  feet  below  the  top  of  the  dam  was  put  in.  The  im- 
possibility of  handling  the  w^ater  compelled  the  cessation  of  further 
operations  in  an  open  cut. 

The  next  method  was  to  sink  a  caisson.  A  correct  idea  of  the 
shape  of  the  caisson  and  the  relative  dimensions  would  be  obtained 
if  a  piece  of  stove-pipe,  having  a  length  a  little  greater  than  one-half 
its  diameter,  were  cut  by  a  plane  passing  through  it  parallel  to,  and 
a  little  above,  its  axis,  the  ends  of  the  smaller  segment  so  formed 
closed,  and  the  whole  covered  by  a  nearly  rectangular  box. 

The  caisson  was  41^  feet  by  24  feet  10  inches  outside  at  the 
bottom,  22  feet  high  outside,  and  the  sides  had  a  batter  of  2  feet. 
The  interior  chamber  was  40^  feet  in  diameter  and  17  feet  from 
the  crown  of  the  arch  to  the  centre  of  the  chord ;  the  radius  of  the 
arch  was  20^  feet. 

The  arch  of  the  caisson  was  composed  of  yellow-pine  timbers  6 
feet  long,  10  inches  thick,  and  12  inches  wide.  These  were  broken- 
jointed  and  bolted  together  with  four  ^-inch  bolts  through  each. 
Placed  in  the  interior  was  a  lagging  of  planks  4  by  10  inches,  which, 
after  being  well  calked,  was  covered  with  sheets  of  lead  and  as- 
phalt to  render  it  impervious  to  water.  The  ends  of  the  caisson 
were  made  of  double  timbers  running  in  different  directions,  which 
were  held  firmly  against  the  horizontal  braces  of  the  inside,  and  the 


28  TUNNELING  UNDER   THE  HUDSON   RIVER. 

roof  by  17  bolted  iron  rods.  Rods  also  extended  in  a  transverse  direc- 
tion and  bolted  to  the  exterior  to  prevent  spreading.  The  spaces 
between  the  top  of  the  arch  and  the  corners  of  the  box  were  entirely- 
filled  with  concrete  to  give  additional  weight  and  strength.  An 
open  box  about  12  feet  deep  was  built  on  top  of  the  caisson,  and 
was  filled  with  the  excavated  earth  in  order  to  obtain  weight  to  sink 
it.  The  construction  of  the  caisson  is  clearly  illustrated  in  Plates 
VII.  and  VIII.;  it  was  designed  by  Mr.  Anderson. 

Through  the  roof  of  the  caisson  extended  two  air-locks — the 
smaller  was  2l/2  feet  in  diameter  and  was  for  supplies;  the  other  was 
5  feet  in  diameter  at  the  lower  end  and  6  feet  at  the  top.  These  were 
built  of  plates  of  boiler-iron,  which  were  added  section  by  section  as 
the  caisson  descended. 

The  larger  lock  was  placed  near,  and  about  in  the  centre  of,  the 
western  wall  of  the  caisson.  The  section  5  feet  in  diameter  ex- 
tended from  the  roof  nearly  to  the  surface  of  the  ground,  where  it 
expanded  to  6  feet  in  diameter.  On  top  was  formed  a  circular 
chamber  6  feet  high  by  6  feet  across,  and  attached  to  one  side  of 
which  was  a  circular  elbow  4  feet  long  by  5  feel  across.  In  this  por- 
tion three  circular  doors,  2  feet  10  inches  in  diameter  in  the  clear, 
were  hung — one  at  the  outer  end  of  the  elbow,  one  between  the  el- 
bow and  the  inner  chamber,  and  one  at  the  lower  side  of  the 
chamber  on  top  of  the  tube.  The  object  in  having  three  doors 
so  located  was  to  provide  a  large  lock  to  be  used  when  chang- 
ing shifts  or  in  case  a  blowout  should  drive  many  men  up  the 
shaft.  The  smaller  lock  was  used  when  three  or  four  entered, 
and  by  it  the  passage  could  be  made  without  losing  so  much 
air.  The  corners  were  stayed  as  shown  in  Plate  IX.  Leading  from 
the  lock  down  to  the  caisson-chamber  were  two  ladders.  V>\  this 
method  of  construction  the  men  were  afforded  a  safe  retreat  in  case 
of  accident. 

During  the  lowering  of  the  caisson  the  water  was  expelled  by 
air,  the  pressure  being  increased  as  the  depth  became  greater.  Each 
of  the  north  and  south  sides  of  the  caisson  was  upheld  by  three 
wrought-iron  shoes  6  inches  wide,  1  inch  thick,  and  bent  so  as  to 
clasp  the  under  edge  of  the  side.  From  these  the  screw  suspension- 
rods,  3  inches  in  diameter,  extended  to  three  pairs  of  heavy  timbers 
which  projected  about  1  foot  over  the  sides  of  the  coffer-dam  and  ran 


TUNNELING   UNDER  TIIE   HUDSON   RIVER.  29 

back  upon  the  surface  of  the  ground  30  feet,  the  ends  being  loaded 
with  rails.  This  arrangement,  shown  in  plan  in  Plate  V 11.,  gave 
ample  strength  to  sustain  the  weight  of  the  entire  structure  and  pre- 
vented a  too  rapid  descent.  The  caisson  was  lowered  by  digging 
away  cinder  the  edges,  and  then,  after  having  reduced  the  air-pres- 
sure, the  suspension-rods  were  lengthened.  In  October,  1880,  the 
caisson  reached  the  requisite  depth,  42  feet  below  the  top  of  the 
shaft,  or  38  feet  below  mean  high  tide.  As  the  old  connecting- 
chamber  was  cleaned  out  the  bodies  of  the  twenty  men  who  had 
perished  in  the  July  accident  were  recovered. 

When  a  trench  had  been  dug  under  the  edges  of  the  caisson 
and  the  rods  lengthened  the  air-pressure  was  reduced.  The  air 
served  as  a  cushion  which  supported  the  greater  part  of  the  weight 
of  the  structure  and  its  load,  the  side-rods  regulating  the  rapidity  of 
the  downward  motion  and  guiding  the  caisson.  The  amount  of  the 
reduction  necessary  to  effect  a  movement  varied  with  the  friction  of 
the  sides  through  the  silt,  the  clinging  power  of  which  was  tremen- 
dous ;  the  longer  the  time  in  which  the  silt  had  to  settle,  the  greater 
the  friction.  The  caisson  weighed  4G0  tons  ;  the  box  of  earth  on  top 
weighed  350  tons  ;  the  locks  and  connections  45  tons  ;  iron  rails  and 
bricks  that  were  placed  on  top  weighed  250  tons — making  a  total 
weight  of  1,105  tons.  The  caisson  was  of  sufficient  strength  to  have 
withstood  the  pressure  of  the  earth  surrounding  it,  even  if  all  the 
air  had  escaped.  When  the  vertical  struts  were  being  placed  in 
position  one  of  the  last  acts  was  to  drive  small  wedges  of  soft  pine 
between  them  and  the  roof,  designed  to  serve  as  indicators  in  regard 
to  a  yielding  to  strains.  These  were  frequently  examined,  but  at  no 
time  could  the  slightest  change  be  observed.  The  weak  parts  of  the 
caisson  were  the  two  ends,  which  were  made  of  horizontal  and  verti- 
cal timbers  resting  against  eight  struts  1  foot  square,  extending  the 
length  of  the  caisson  and  braced  by  3  transverse  beams  and  9  ver- 
tical struts.- 

A  calculation  was  published  by  the  writer  at  that  time  to  show 
the  greatest  strain  that  could  possibly  come  upon  the  braces.  The 
area  of  the  circular  segment  of  each  end  was  514.4  square  feet.  This 
was  calculated  from  the  inner  dimensions  of  the  arch.  Considering 
this  as  being  at  an  average  depth  of  35  feet,  and  the  mixture  of  silt  and 
water  as  weighing  90  pounds  per  cubic  foot,  if  not  sustained  by  com- 


30  TUNNELING  UNDER  THE  HUDSON  RIVER. 

pact  silt — and  it  was  not  probable  that  it  would  receive  much,  if  any, 
support  from  this,  since  it  had  not  settled  firmly — there  would  be  a 
pressure  exerted  upon  the  segment  of  1,620,293  pounds,  or  810  tons, 
or  3,150  pounds  per  square  foot.  The  lower  central  strut  supported 
an  area  of  about  42  square  feet,  and,  consequently,  a  combined  pres- 
sure of  132,300  pounds.  The  two  adjoining  struts  had  to  sustain  an 
area  of  at  least  77  square  feet  and  a  pressure  of  242,550  pounds. 
This  strain  would  have  been  by  no  means  excessive  and  would  have 
left  a  wide  margin  of  safety. 

After  the  sinking  of  the  caisson  the  great  problem  was  to  form 
a  connection  between  it  and  the  shaft,  and  also  between  it  and  the 
completed  portion  of  the  tunnels.  The  case  created  much  interest 
among  engineers,  many  of  whom  criticised  the  plans  very  freely 
and  had  no  hesitancy  in  predicting  that  work  would  never  be  re- 
sumed unless  the  methods  were  changed. 

Operations  were  directed  toward  opening  the  old  air-lock,  the 
door  of  which  was  but  about  2  feet  from  the  west  side  of  the  caisson. 
To  do  this  a  rectangular  opening,  just  large  enough  to  admit  a  plate, 
was  cut  in  the  side  of  the  caisson  next  the  shaft,  and  the  plate  teles- 
coped on  to  the  projecting  part  of  the  air-lock.  A  second  opening 
was  cut  next  to  the  first,  and  a  second  plate  inserted  ;  this  was  con- 
tinued until  a  perfect  circle  had  been  formed,  when  the  centre  piece 
was  removed  and  the  plates  securely  bolted  to  each  other  and  to  the 
side,  and  the  interstices  filled  with  silt.  Air  was  then  admitted  to 
the  lock,  the  outer  door  having  been  closed  and  the  plate  removed 
which  had  wedged  the  inner  door  at  the  time  of  the  accident. 
Opening  this  lock  greatly  facilitated  subsequent  movements,  since  it 
was  both  easier  and  quicker  to  lower  supplies  down  the  shaft,  and 
pass  them  through  the  old  lock,  than  it  was  to  admit  them  through 
the  vertical  lock. 

It  was  decided  to  extend  the  two  tunnels  to  the  shaft,  and  not 
finish  the  upper  half,  but  leave  the  whole  as  one  large  chamber 
uniting  the  two.  The  lower  portion  of  the  tunnel  had  been  so  far 
finished  that  the  caisson  extended  about  8  feet  over  it,  and  the 
sides  slanted  until  the  top  was  about  4  feet  from  the  outside. 
Building  the  invert,  which  was  also  to  serve  the  purpose  of  in- 
vert for  each  tunnel,  required  great  skill  and  extreme  caution.  A 
hole  4  feet  square  was  started  in  the  southeast  corner,  and  as  it 


Plate  VII. 


Plate  IX. 


CAISSON.-  NEW  JERSEY  SIDE. 


.uv 


TUNNELING   UNDER  THE  HUDSON   RIVER.  31 

was  sunk  the  sides  were  planked  and  braced  to  secure  the  air. 
After  iht;  bottom  had  been  reached,  8  feet  below  the  shoe,  the  brick- 
work was  started  and  built  up  on  plates  previously  set,  until  that 
part  of  the  caisson  rested  upon  a  secure  foundation.  The  same 
was  done  at  the  northeast«corner.  A  little  at  a  time,  and  with  great 
care,  these  plates  were  carried  along  the  entire  north  and  south 
sides,  thereby  forming  a  secure  wall  to  resist  the  air-pressure. 
They  were  also  carried  over  until  the  east  side  rested  on  masomy, 
except  about  10  or  12  feet  in  the  centre.  A  bulkhead  was  gradu- 
ally built  under  this  side  down  to  the  bottom,  when  the  dividing 
wall,  or  centre  column,  was  extended  and  the  work  of  excavating 
the  centre  begun. 

Plates  6  feet  long  by  2  feet  wide  had  been  telescoped,  in  the 
same  manner  as  already  described  in  connecting  the  old  air-lock, 
from  the  eastern  side  of  the  caisson  over  the  top  of  the  tunnel,  and 
securely  bolted.  Upon  the  western  side  a  bulkhead  had  been  built 
to  the  bottom,  and  heavy  beams  extended  from  side  to  side.  It  was 
early  found  necessary  to  bulkhead  the  openings  to  the  two  tunnels, 
so  that  the  masonry  in  the  caisson  might  be  completed. 

The  caisson  was  not  sunk  so  as  to  evenly  cover  the  two  tunnels, 
as  will  be  seen  in  Plate  XL  One  shoe  was  in  line  with  the  exterior 
of  one  tunnel,  while  the  other  was  about  3  feet  from  the  tunnel. 
The  masonry  was  built  out  to  reach  the  sides,  and  projections  were 
formed  for  the  shoes  to  rest  upon.  A  masonry  arch  was  built  3 
feet  thick  inside  the  arch  of  the  caisson,  and  between  this  arch  and 
the  top  of  the  tunnel  was  placed  a  brick  bulkhead.  This  construc- 
tion is  very  plainly  indicated  in  the  above-named  drawing.  The  op- 
posite or  west  side  of  the  caisson  was  also  bricked  up  from  the  bot- 
tom of  the  tunnel  to  the  arch  ;  this  wall  was  afterward  removed 
when  the  tunnels  were  joined  to  the  shaft.  Thus  the  caisson  was 
converted  into  a  large  working-chamber,  connected  with  the  outer 
world  by  three  air-locks,  and  Avholly  enclosed  by  masonry. 

All  the  interior  bracing  of  the  caisson  that  did  not  interfere  with 
the  work  was  left  in,  and  as  fast  as  the  excavations  were  made  both 
vertical  and  horizontal  struts  were  rjut  in.  A  working-platform  was 
erected,  upon  which  were  the  water-tanks,  cement- trough,  bricks,  etc. 
Rosendale  cement,  in  the  proportion  of  one  cement  to  one  and  one-half 
sand,  was  used  ;  it  was  mixed  dry  outside  and  brought  in  in  bags. 


CHAPTER  V. 

RESUMING  WORK— ILLUMINATION— CONDITION  OF  ATMOSPHERE— 
AIR-OOM  PRESSORS — STEAM  SUPPLY — TELEPHONE — SUPPLYING  MA- 
TERIAL—  REMOVING  EXCAVATED   MATERIAL. 

The  caisson  having  been  made  perfectly  secure,  the  next  aim 
was  to  resume  work  on  the  tunnels.  It  was  well  known  that  a  grave 
obstacle  would  be  presented  when  the  attempt  was  made  to  open 
the  south  tunnel,  which  had  been  completed  but  a  short  distance 
from  the  end  of  the  connecting-chamber,  and  a  few  feet  beyond 
which  was  the  crib-work  of  the  docks,  through  which  water  had 
ebbed  and  flowed  since  the  day  of  the  accident.  That  section  adja- 
cent to  the  caisson  bulkhead  had  been  compactly  filled  with  silt,  as 
just  described,  but  beyond  that  no  reliance  could  be  placed  upon 
compressed  air,  as  the  consistency  of  the  silt  which  had  been  arti- 
ficially thrown  in  decreased  rapidly. 

A  hole  6  feet  in  diameter  was  cut  through  near  the  top  of  the 
bulkhead,  and  flanged  iron  plates  2  feet  wide  were  put  in  and  bolted. 
This  small  tunnel  was  constructed  in  a  manner  precisely  similar  to 
that  by  which  the  large  tunnel  was  advanced — plate  by  plate. 
When  the  soft  silt  was  met  a  piston  was  loosely  fitted  in  the  pilot. 
In  this  was  placed  a  pipe,  3}4  inches  in  diameter,  through  which  silt 
could  be  forced.  The  piston-rod  extended  across  the  caisson  to  the 
opposite  wall,  and  was  operated  by  two  hydraulic  jacks.  By  this 
system  of  ramming  the  desired  compactness  was  obtained  at  the 
head  of  the  pilot. 

When  the  crib- work  was  reached  it  was  found  that  air  would 
occasionally  escape  through  the  spaces  between  the  loose  filling. 
The  application  of  a  ball  of  silt  would  stop  a  small  leak,  but  in 
large  openings  a  bag  of  cement  was  forced  up,  when  the  air-pressure 
would  hold  it  in  position. 

Practically  the  work  was  now  in  the  same  state  as  at  the  time  of 
the  accident,  with  the  important  exception  that  the  temporary  en- 
trance had  been  replaced  by  a  substantial  chamber  of  masonry  and 
additional  facilities  had  been  made  for  entering  the  tunnel. 


34  TUNNELING  UNDER  THE  HUDSON   RIVER. 

We  have  not  attempted  to  describe  any  of  the  machinery  or  the 
mode  of  getting  in  supplies  and  removing  waste  material ;  it  was 
thought  better  to  delay  this  until  the  work  had  been  reopened. 

For  general  illumination  of  the  tunnel  the  electric  light,  which 
was  early  introduced  and  continued  through  all  the  operations,  proved 
most  satisfactory,  one  lamp  lighting  up  very  brilliantly  a  distance 
of  from  100  to  150  feet.  Its  power  depended  upon  the  clearness  of 
the  atmosphere  in  the  work  ;  the  haziness,  which  prevailed  to  a 
certain  extent  all  the  time,  coupled  with  the  almost  total  absence  of 
reflecting  surfaces,  compelled  the  adoption  of  candles,  which  were 
used  by  the  men  to  light  all  spaces  which  were  shadowed.  The 
masons  had  to  use  candles  even  when  working  directlv  beneath  or 
alongside  of  the  electric  light  when  the  rays  from  the  latter  were  in- 
tercepted by  a  brace  or  other  obstruction.  Only  the  arc  light  was 
tried. 

The  dynamo  and  lamps  were  from  the  United  States  Electric 
Lighting  Company  ;  in  the  first  lamps  the  carbons  were  ^  of  an  inch 
in  diameter  by  12  inches  long.  Ordinary  coach  candles  iy2  inches 
long,  \%  inches  in  diameter,  and  weighing  5  ounces,  were  used. 
These  candles  burned  at  the  same  rate  inside  as  out  of  the  tunnel. 

As  the  heading  was  advanced  the  lamps  were  distributed  along 
the  tunnel,  the  object  being  to  light  the  working-chamber  where  the 
locks  were  and  the  heading  as  brightly  as  possible,  and  illuminating 
the  intervening  space  just  enough  for  the  workmen  to  easily  find 
their  way.  Arising  from  the  electric  lamps  and  the  candles  there 
was  much  carbon-dust  floating  in  the  air  ;  tins  collected  in  the  nose, 
but  was  freely  expelled  by  a  vigorous  blowing  ;  it  caused  no  ill 
effects  whatever. 

Telephone- wires  connected  the  working-chamber  (Plate  XI.) 
with  the  office.  The  Bell  telephone  and  Blake  transmitter  were 
used,  the  sounds  being  very  distinct  at  each  end  of  the  line,  bnfc 
owing  to  the  noise  at  the  inner  end  it  was  found  expedient  to  place 
the  instrument  in  a  small  closet. 

The  success  of  the  work  at  every  step  depended  upon  there  being 
a  constant  and  ample  supply  of  air — a  supply  which  had  to  be  suffi- 
cient not  only  to  overcome  the  loss  due  to  small  leaks,  but  to  keep 
up  the  required  pressure  in  case  a  large  leak  occurred.  It  was  not 
possible  to  make  and  keep  all  the  joints  perfectly  air  tight,  and 


tun: si: LINO  UNDEU  TIIK  HUDSON   RIVER.  36 

then1  was  always  a  more  or  less  quantity  of  air  making  its  way  out 
through  the  silt;  besides  this,  the  continuous  use  of  the  locks  and 
the  method  of  removing  the  waste  silt— which  will  be  described 
shortly — required  a  large  amount  of  air.  Within  certain  limits  the 
free  use  of  the  air  in  the  tunnel  was  not  considered  as  an  obstacle, 
since,  by  its  introduction  at  the  heading  and  its  escape  at  the  rear 
end  of  the  work  through  the  blow-out  pipe  and  the  locks,  a  circula- 
tion was  kept  up  which  insured  a  pure  atmosphere  in  all  parts. 

At  the  time  of  which  we  are  writing  two  air-compressors,  used 
alternately,  formed  a  part  of  the  plant — a  double-acting  Clayton 
compressor,  having  two  air  and  two  steam  cylinders,  each  10  inches 
in  diameter,  and  a  stroke  of  13  inches  ;  a  double-acting  Ingersoll 
rock-drill  compressor,  having  single  cylinders,  the  diameter  of  the 
steam- cylinder  being  10  inches,  the  air-cylinder  12  inches,  and 
the  stroke  12  inches.  In  actual  practice  the  first  machine  com- 
pressed 1.65  cubic  feet  of  air  at  each  revolution  ;  the  second  1.05 
feet  at  each  revolution.  A  short  time  before  the  accident,  when  the 
needed  pressure  was  18  pounds  per  square  inch,  there  were  83,000 
cubic  feet  of  normal  air  delivered  into  the  tunnel  every  twenty-four 
hours  ;  this  giving  about  150  cubic  feet  of  normal  air  per  hour  to 
each  man  at  work. 

Air  from  the  compressors  was  delivered  to  an  air-reservoir  built 
of  boiler-iron,  located  near  the  shaft,  and  which  was  provided  with 
a  mercury -gauge  to  indicate  the  pressure.  The  delivery-pipe  led 
from  the  reservoir,  down  the  shaft,  through  the  air-lock,  and  along 
the  completed  work  to  the  heading.  All  the  air  was  washed  twice 
— once  as  it  was  drawn  into  the  cylinders  of  the  compressors,  and 
again  as  it  passed  through  water  into  the  reservoir. 

A  steam-pipe  led  from  the  boilers  to  a  force-pump  near  the  old 
air-lock,  supplying  first  a  donkey-pump,  then  the  electric-light  ma- 
chine and  the  air-compressors.  After  the  working-chamber  had 
been  completed  both  a  steam  and  air  supply  pipe  were  passed 
through  the  vertical  lock,  the  former  to  run  the  engine  used  to  draw 
up  the  cars. 

In  Plate  VI.  is  shown  a  brick-chute,  by  means  of  which  bricks 
were  delivered  on  the  platform  in  the  shaft.  It  was  a  wooden  box 
placed  in  an  inclined  position,  and  having  upon  the  under  surface 
of  the  upper  side  hinged  leaves  which  retarded,  without  stopping, 


36  TUNNELING   UNDER  THE  HUDSON    RIVEE. 

the  descent  of  the  brick,  thereby  insuring  its  safe  arrival  at  the  bot- 
tom. The  cement  was  also  sent  through  a  chute  to  the  platform. 
Both  the  brick,  and  cement  which  was  mixed  with  the  sand  and 
tied  up  in  bags,  were  loaded  on  cars  running  upon  a  narrow  track 
which  extended  from  the  shaft  through  the  air-lock  down  to  the 
heading.  A  short,  removable  section  of  track  fitted  over  the  sill 
of  each  lock-door.  The  loaded  car  was  run  into  the  lock,  the  piece 
of  track  removed,  the  door  closed,  and  the  air  from  the  tunnel  ad- 
mitted ;  then  the  inner  door  was  opened,  the  track  made  continu- 
ous, and  the  car  run  out.  In  order  that  one  car  might  be  loading 
during  the  journey  of  the  other  there  were  two  tracks  laid  in  the 
shaft ;  the  shifting  of  the  cars  was  accomplished  by  the  aid  of  a 
sliding  platform.  The  general  style  of  dirt-car  is  shown  in  Plate 
XII.  ;  brick  and  cement  were  carried  in  on  ordinary  platform-cars. 

The  small  lock  extending  through  tlie  roof  of  the  caisson  was 
designed  for  supplies.  Its  lower  end  was  lifted  with  an  extension 
which  was  just  a  quadrant  of  a  circle  ;  its  cross-section  was  square, 
while  that  of  the  remaining  portion  was  circular.  One  door  was 
placed  at  the  lower  end  of  the  lock,  (he  other  at  the  upper  end 
about  3  feet  above  the  ground.  It  was  used  principally  for  brick, 
the  cement,  plates,  etc.,  being  still  taken  in  through  the  old  horizon- 
tal lock.  In  loading  it,  the  lower  door  having  been  closed,  a  barrel 
was  filled  with  bricks  and  lowered  by  a  rope  and  tackle  ;  when 
at  the  head  of  the  lock  the  bottom  was  dropped  from  the  barrel, 
allowing  its  contents  to  fall  out.  The  load  varied  from  50  to  100 
barrels  of  bricks.  After  the  upper  door  had  been  closed  the  lower 
one  was  opened,  when  the  bricks  fell  upon  the  platform  of  the 
working-chamber.  They  were  then  taken  to  the  heading  upon 
a  platform-car  running  upon  a  track  extending  down  the  north  side 
of  the  tunnel — the  track  for  the  silt-car  being  upon  the  south  side. 

The  economical  and  rapid  removal  of  the  excavated  silt  Avas  a 
question  of  great  importance.  Previous  to  the  accident  a  6-inch 
blow-out  pipe  (Plate  YI.)  extended  through  the  air-lock  to  the 
heading,  the  end  being  provided  with  a  movable  section  and  valve. 
Silt  and  water  were  mixed  in  a  suitable  receptacle  into  which  the 
end  of  the  pipe  was  dipped  ;  upon  tlie  valve  being  opened  the  air- 
pressure  forced  the  mixture  out  of  the  tunnel.  The  bottom  of  the 
shaft  was  first  used  as  a  receiver,  but  afterward  a  waste-tank  upon 


TUNNELING   UNDER  THE   HUDSON   RIVER.  37 

the  surface  of  the  ground  was  designed.  The  silt  was  then  lifted  up 
the  shaft  in  buckets  and  dumped  into  cars,  which  were  drawn  upon 
a  narrow-gauge  track  running  to  the  low  land  just  back  of  the  work, 
and  there  emptied.  A  covered  tank  was  so  constructed  that  the  car 
could  be  run  under  a  delivery-spout  to  be  loaded,  the  tank  being 
filled  through  the  blow-out  pipe. 

As  the  tunnel  was  advanced  it  became  necessary,  owing  to  the 
increased  friction  in  the  pipe,  to  adopt  some  new  plan  for  doing  this 
work.  The  completed  work  was  left  a  little  more  than  one-half  full  of 
excavated  silt,  the  intention  being  to  remove  this  after  the  approaches 
had  been  opened,  when  it  could  be  handled  more  easily,  quickly,  and 
cheaply  ;  in  the  meantime  it  served,  by  its  weight,  to  keep  the  new 
sections  in  position  until  the  masonry  had  set.  Upon  the  silt  was 
laid  a  narrow-gauge  track,  upon  which  ran  a  dumping-car  (Plate 
XIII.) having  a  capacity  of  iy2  cubic  yards.  The  silt  taken  from  the 
heading  was  then  placed  in  this  car,  which  was  drawn  up  by  a  small 
engine  located  near  the  west  wall  of  the  working-chamber.  At  the 
upper  end  of  the  track  there  was  a  sharp  incline  of  about  45  de- 
grees, the  rails  on  which  were  placed  just  wide  enough  to  permit 
the  front  wheels  of  the  car  to  pass  between  and  remain  on  a  horizon- 
tal track ;  the  rear  wheels,  having  faces  two  or  three  inches  wider 
than  those  in  front,  ascended  the  incline,  when  the  bottom  of  the  car 
sloped  sufficiently  to  allow  its  load  to  slide  off  into  a  well.  (The 
operation  of  this  car  is  shown  very  distinctly  in  Plate  X.)  The 
silt  was  then  mixed  with  water  and  blown  out  by  the  air  to  the  re- 
servoir above  ground. 

An  Eads  sand-pump,  the  suction-pipe  of  which  entered  a  box 
provided  with  a  buffer,  was  introduced.  The  silt  was  spread  over 
a  wire  screen  at  the  bottom  of  the  latter,  and,  being  mixed  with 
water,  was  discharged  directly  into  the  open  air,  thus  doing  away 
with  the  conveyance  of  the  silt  to  the  working- chamber  on  cars. 
The  water  and  compressed  air  together  disposed  of  the  silt  very  ef- 
fectually, and  delivered  it  much  faster  than  it  could  be  supplied  at 
the  then  (July,  1881)  rate  of  excavation. 

At  one  time,  when  the  silt  had  been  nearly  blown  out  of  the  well 
at  the  working-chamber,  and  the  end  of  the  pipe  almost  uncovered, 
it  was  found  impossible  to  turn  the  valve,  some  obstruction  having 
clogged  it.     In  the  next  instant  the  silt  had  all  been  driven  out, 


38  TUNNELING   UNDER  THE   HUDSON   RIVER. 

and  the  air,  making  a  terrific  noise,  rushed  up  the  pipe.  The  men 
made  haste  for  the  air-lock,  being  led  in  their  endeavors  by  one  of 
the  bosses.  The  superintendent,  who  chanced  to  be  present,  seized 
a  shovel  and  placed  it  over  the  end  of  the  pipe,  against  which  it  was 
tightly  forced  by  the  pressure  of  the  air.  As  soon  as  the  upward 
current  had  been  stopped  a  piece  of  brick  which  had  lodged  in  the 
valve  dropped,  when  the  escape  was  shut  off.  This  incident  is 
merely  given  to  show  how  ready  workmen  engaged  upon  undertak- 
ings of  this  character  are  to  take  alarm.  They  knew  they  were  in  a 
perfectly  safe  chamber,  and  they  also  knew  that  it  would  take  some 
time  for  all  the  air  to  escape  and  the  water  to  reach  them  ;  but  or- 
dinary workmen  cannot  be  expected  to  stop  and  reason,  especially 
when  the  retreat  is  ably  led  by  one  of  their  superiors. 

The  one  who  would  attempt  to  direct  operations  in  an  undertak- 
ing of  this  kind  must  be  gifted  with  both  physical  and  mora]  courage  ; 
he  must  not  feel — for  if  he  feels  he  will  surely  show — any  timidity,  and 
he  must  exercise  such  an  influence  over  his  subordinates  that  they 
will  have  confidence  in  him.  in  themselves,  and  in  the  success  of  his 
plans.  He  must  have  presence  of  mind  ;  he  must  quickly  perceive 
and  accurately  realize  the  difficulty,  and  must  unerringly  judge  of 
and  adopt  the  best  possible  solution.  While  being  willing  to  at- 
tempt extreme  measures  in  extreme  cases,  he  ought  never  to  be  will- 
ing to  jeopardize  his  men  or  his  work.  Carefulness,  thoughtful- 
ness,  and  thoroughness  must  not  be  sacrificed  for  speed.  While 
work  was  being  carried  on  in  the  caisson  Mr.  Anderson,  becom- 
ing tired  out,  stretched  himself  upon  some  cement-sacks  and  went 
to  sleep.  The  work  was  uncertain,  and  the  men  were  in  such  a  con- 
dition as  to  become  easily  alarmed.  In  doing  this  he  had  two  ob- 
jects in  view :  he  wanted  to  be  instantly  on  hand  in  case  anything 
happened,  and  he  wanted  particularly  to  inspire  confidence  in  his 
men.  When  he  was  awakened  he  was  surprised  at  the  amount  of 
work  which  had  been  done  and  the  renewed  cheerfulness  of  his 
assistants.  One  of  them  described  the  result  to  the  writer  as  fol- 
lows: "  We  thought  it  was  all  right  when  the  boss  went  to  sleep  in 
there." 


CHAPTER  VI. 

SHAPE,  DIMENSIONS,  AND  USE  OF  PILOT — ADVANCING  HEADING — 
OBJECTS  OF  IKON  SHEATHING — MASONRY — LEAKS — BULKHEADS  IX 
TUNNELS — CONNECTING  WORKING-CHAMBER  WITH  SHAFT — PER- 
FECTED METHOD  OF  OBTAINING  SUPPLIES  AND  REMOVING  SILT — 
SUSPENSION   OF   WORK   ON   NEW    JERSEY    SIDE. 

In  extending  the  work  before  the  accident  the  outer  sheathing  of 
plates  was  put  in  position  as  soon  as  the  excavation  was  made,  and 
was  in  part  held  by  struts  resting  upon  the  bottom  and  sides  ;  this 
excluded  the  silt  while  the  masonry  was  being  built.  Although  the 
utmost  celerity  was  practised  in  getting  the  plates  and  struts  in  posi- 
tion, the  shell  would  at  times  be  forced  down  and  out  of  place  suffi- 
ciently to  make  it  almost  impossible  to  maintain  an  accurate  align- 
ment, as  we  have  already  noticed.  This  was  because  the  silt  was 
not  always  of  the  same  degree  of  compactness.  At  some  points  a 
material  of  a  looser  character  was  met,  which,  not  having  the  sustain- 
ing power  of  pure,  undisturbed  silt,  would  exert  a  greater  pressure 
upon  the  shell  and  bear  it  down.  The  expedient  of  inserting  the 
plates  higher  than  they  should  be  was  tried,  but  the  variations  in  the 
weight  of  the  upper  material  and  its  slight  changes  in  density,  to- 
gether with  the  fluctuations  of  the  resisting  pressure,  constituted 
data  which  were  unreliable  and  from  which  no  satisfactory  results 
could  be  obtained.  Nor  was  there  any  method  by  which  the  precise 
nature  of  every  part  of  the  surrounding  envelope  could  be  deter- 
mined and  the  amount  of  its  settlement  gauged. 

It  therefore  became  necessary  to  introduce  some  device  by  which 
a  firm  foundation  could  be  secured  for  the  struts  to  rest  upon.  All 
the  features  which  should  be  embodied  in  such  a  device  seemed  to 
be  present  in  the  "'pilot,"*  shown  in  place  in  the  heading  in  the 
longitudinal  elevation  and  cross-section,  Plate  XIV.  This  pilot  was 
an  iron  tube,  built  up  of  plates,  and  of  such  a  diameter  as  not  to 
seriously  occupy  the  space  in  the  tunnel,  and  having  a  length  suffi- 
cient to  permit  its  forward  end  to  enter  some  distance  into  the  head- 

*  The  "  pilot "  was  invented  by  Mr.  Anderson. 
39 


40  TUNNELING  UNDER  THE  HUDSON   RIVER. 

ing  and.  its  rear  end  to  be  abreast  the  completed  tunnel  or  masonry  ; 
tlie  intermediate  points  served  as  a  centre  from  which  to  brace  the 
plates. 

It  was  composed  of  ten  segmental,  interchangeable  plates  4  feet 
long,  22  inches  wide,  and  %  inch  thick,  united  by  means  of  angle- 
irons  riveted,  to  the  inner  sides  along  the  longitudinal  edges ; 
curved  angle-irons  were  also  riveted  to  the  ends  of  each  plate.  In 
the  joints  were  placed  thick  iron  plates,  which,  projecting  a  few 
inches  from  the  outer  surface  of  the  cylinder,  formed  series  of  trans- 
verse and  longitudinal  ribs  which  added  greatly  to  its  strength. 
Struts  rested  against  the  pilot  next  to  the  transverse  plates,  and  sup- 
ported the  outer  shell  and  masonry  of  the  tunnel,  and  also  the  rear 
end  of  the  pilot,  which  extended  into  the  finished  work.  The  plates 
were  bolted  together,  and,  as  they  were  interchangeable,  it  was  only 
necessary  to  have  enough  to  make  a  tube  of  from  50  to  60  feet  in 
length — 25  or  30  feet  being  in  advance  of  the  heading  and  the  re- 
mainder in  the  rear. 

The  longitudinal  ribs  stiffened  the  pilot,  while  the  transverse  ribs 
not  only  stiffened  it  but  also  acted  as  anchors  to  keep  it  in  advance 
of  the  heading,  for  the  enormous  pressure  tended  to  force  it  back 
into  the  completed  section.  When  operating  in  material  that  will 
flow  rapidly  when  mixed  with  a  small  quantity  of  water — as  was 
the  case  with  this  silt — the  tendency  of  the  material  is  to  run  back 
along  the  smooth  exterior  of  the  pilot  and  thence  down  the  heading. 
To  obviate  this  the  transverse  joint-plates  were  adopted,  and,  as  they 
could  have  been  made  of  any  width,  it  wras  always  easy  to  obtain  a 
surface  of  sufficient  area  to  prevent  any  disposition  of  the  earth  to 
slide  back  along  the  cjdinder. 

By  keeping  the  end  of  the  pilot  well  in  advance  of  the  heading 
the  ground  through  which  the  latter  had  to  pass  was  very  thorough- 
ly explored,  and  Avhen  any  soft  spots  or  "pockets"  were  encoun- 
tered they  were  much  more  easily  and  safely  controlled  than  they 
could  have  been  without  the  pilot.  This  was  due  to  the  fact  that 
the  exposed  surface  at  the  head  of  the  pilot  was  but  6  feet  in  dia- 
meter, while  that  at  the  head  of  the  tunnel  was  21  by  23  feet. 

In  building  tunnels  through  loose  materials  it  has  been  custom- 
ary to  bank  the  head  in  order  to  form  resting-places  for  the  braces 
to  support  the  crown  of  the  arch.     The  immense  pressure  would 


SECTION 

N       l*S.      THROUGH 

(EST      END     OF      CAISSON 


Plate  XII. 


Plate  XIII 


Plate  XIV, 


' 


VIX 


TUNNELING    UNDER  THE  HUDSON   KIVKR.  41 

oaase  these  to  give  way,  and  the  large  number  of  braces  would  so 
fill  the  working  space  as  fco  interfere  considerably  with  the  men. 
The  pilot  absolutely  prevented  the  earth  at  the  heading  from  caving 
in,  because  the  upper  portion  of  the  earth  rested  upon  the  pilot,  and 
the  space  between  the  bottom  of  the  pilot  and  the  bottom  of  tun- 
nel was  not  large  enough  to  allow  the  earth  to  slide.  As  all  the 
braces  were  radial  ones,  they  were  very  much  shorter  than  the 
radius  of  the  tunnel,  and,  consequently,  were  of  much  smaller  cross- 
section,  and  were  more  conveniently  and  rapidly  handled  than  could 
have  been  the  heavy  braces  used  with  tunnel-shields  or  with  a 
banked  heading. 

There  was  ample  room  at  the  head  of  the  pilot  for  two  men  to 
work  without  interfering  with  each  other.  In  commencing  a  ring  a 
space  at  the  crown  was  dug  out  until  a  plate  could  be  put  in  ;  this 
plate  was  bolted  to  the  ring  already  completed.  An  excavation  was 
then  made  at  each  side  and  the  second  and  third  plates  inserted. 
Plates  were  taken  from  the  rear  and  carried  forward  as  they  were 
needed.  In  this  way  the  ring  was  built  down  each  side  and  across 
the  bottom.  The  transverse  and  longitudinal  ribs  were,  of  course, 
put  in  as  the  plates  were  raised.  The  excavated  material  was  wheeled 
back  and  either  thrown  through  side  openings  in  the  pilot  into  the 
finished  section  of  masonry,  or  taken  to  the  rear  and  there  placed 
upon  cars,  to  be  removed  in  the  usual  way.  The  object  in  making 
holes  in  the  pilot  was  to  diminish  the  distance  to  be  traveled  by  the 
men,  thus  lessening  the  time  required  to  accomplished  a  certain  dis- 
tance. A  two-board  walk  was  laid  from  the  inner  end  to  the 
silt. 

Actual  experience  demonstrated  that  the  iron  in  the  pilot  was 
not  of  sufficient  strength  to  resist  the  strain  that  came  upon  it,  and 
the  thickness  of  the  plates  was  increased  to  ^  of  an  inch.  The 
pilot  was  firmly  supported  at  each  end,  but,  owing  mainly  to  its 
uncommon  length,  the  central  section  was  deflected  when  from  any 
cause  an  excessive  weight  was  brought  to  bear  upon  it ;  and  al- 
though it  sustained  the  radiating  struts  and  received  from  them  ad- 
ditional strength,  this  was  not  enough  to  insure  the  requisite  rigid- 
ity throughout  its  entire  length. 

A  very  clear  idea  of  the  method  of  advancing  the  heading,  as 
finally  adopted,  may  be  obtained  from  Plates  X.  and  XIV.       A 


42  TUNNELING   UNDER  THE  HUDSON   RIVER. 

space  being  opened  at  the  top,  a  plate  was  put  up,  bolted  to  the  one 
previously  set,  and  supported  by  a  brace  resting  on  the  pilot.  As 
far  as  possible  these  braces  were  so  located  that  their  ends  would  be 
alongside  of  the  transverse  ribs  and  not  in  the  middle  of  a  pilot- 
plate. 

Each  ring  was  composed  of  fourteen  plates  }i  of  an  inch  thick 
and  2*4  feet  wide.  The  six  upper  plates  were  3  feet  long  and 
weighed  about  170  pounds  each,  and  the  other  plates  were  6  feet 
long  and  weighed  about  320  pounds  each.  These  weights  include 
the  3-inch  angle-iron  that  was  riveted  to  each  edge  with  ^-inch 
rivets  placed  6  inches  between  centres.  The  plates  were  fastened 
together,  so  as  to  break  joints,  with  ^-inch  bolts  placed  9  inches 
between  centres. 

This  sheathing  was  not  designed  to  act  merely  as  a  thin  lining 
to  prevent  the  passage  of  air  or  water,  out  or  in  ;  but,  owing  to  the 
thickness  of  the  plates,  the  evenly-distributed  pressure  of  the  air 
upon  the  interior,  the  pressure  of  the  silt  upon  the  exterior,  and 
particularly  to  the  stiffening  effect  of  the  angle-irons  that  were  riv- 
eted to  each  edge,  this  coating  had  ample  strength  in  itself  to  sus- 
tain great  and  unequal  pressures  upon  the  various  parts  of  its  sur- 
face. Although  it  was  not  intended  to  support,  unaided,  any  force 
that  might  come  upon  it,  it  was  intended  to  distribute  the  load 
evenly  and  to  bear  the  greatest  possible  weight  when  assisted  by 
the  air-pressure  and  braces. 

At  first  it  was  customary  to  dig  out  a  space  that  would  give 
plenty  of  room  in  which  to  insert  the  plate.  Frequently  an  air- 
pocket  would  be  left  between  the  shell  and  silt,  when  the  latter 
would  begin  a  slow,  regular  movement  toward  the  iron.  Some- 
times wlnm  the  silt  met  the  iron  the  latter  would  be  under  so  great 
a  load  that  it  would  be  forced  to  yield  more  or  less.  To  obviate  this 
difficulty  great  care  was  exercised  in  completely  filling  all  exterior 
holes,  after  the  plates  had  been  inserted  and  braced,  with  either  silt 
or  concrete,  so  that  a  settlement  was  prevented. 

The  excavated  material  was  thrown  into  the  last-completed  sec- 
tion of  tunnel,  and  when  this  had  been  a  little  more  than  half  filled 
the  rest  of  the  material  was  loaded  upon  cars  and  hauled  up  to  the 
working-chamber,  where  it  was  blown  out,  as  previously  described. 
To   facilitate  operations  the  track  was  extended  upon  an  incline 


TUNNELING    QNDER  THE    HUDSON    RIVER.  43 

down  to  the  lower  part  of  the  heading,  which  was  cut  so  as  to  form 
terraces  upon  which  the  workmen  could  stand,  each  gang  being  par- 
ticular to  cut  straight  ahead  in  the  wall  and  to  preserve  the  silt 
platform  upon  which  it  operated. 

As  we  have  often  remarked,  the  advance  was  made  with  extreme 
caution,  to  guard  against  the  too  sudden  opening  of  a  soft  spot, 
where  old  piles  had  been  withdrawn,  containing  water  enough  to 
enable1  it  to  Ih>w  as  quickly  as  quicksand.  A  pocket  Avas  once 
opened  in  the  heading  near  the  arch  of  the  shell.  To  prevent  the 
inflow  of  silt  a  bulkhead  was  put  up  and  braced  from  the  masonry. 
A  hole  was  made  in  the  top  of  the  bulkhead  of  a  size  to  admit  the 
hand,  and  a  dry  ball  of  silt  was  pushed  in.  A  second  was  forced 
in,  crowding  the  first  backward  and  upward  ;  continued  repeti- 
tion of  this  process  formed  a  skin  nearly  impervious  to  air.  This 
skin  was  then  worked  back  with  the  hand,  and  as  it  was  enlarged 
more  balls  were  supplied,  until  the  opening  became  of  the  required 
dimensions  to  admit  a  plate.  During  work  of  this  kind  consider- 
able air  would  sometimes  escape,  making  a  very  unpleasant  noise 
and  threatening  a  reduction  in  pressure  and  a  consequent  disturb- 
ance of  the  bulkhead,  so  that  the  operation  required  men  of  skill, 
courage,  and  coolness. 

When  the  series  of  rings  had  been  placed  the  shell  was  tho- 
roughly cleaned  of  all  dirt  and  the  masons  began  the  brick-work, 
which  was  rapidly  carried  up  the  sides  and  over  the  arch.  The 
masonry  was  built  in  sections  averaging  about  12  feet  in  length. 
For  the  first  450  feet  the  two  tnnnels  were  built  of  hard-burned 
brick  laid  in  the  best  Rosendale  cement,  in  the  proportion  of  one 
cement  to  one  and  one-half  sand,  the  masonry  being  2  feet  thick. 
For  a  short  distance  the  lower  half  of  the  tunnel  was  made  of  solid 
concrete,  and  the  upper  half  was  lined  with  a  5-inch  course  of 
asphalt  blocks  backed  with  brick- work,  as  an  experiment ;  hard- 
bnrned  brick  was  finally  adopted,  as  being  the  best  material  with 
which  to  build  the  wall.  When  the  north  tunnel  had  been  ad- 
vanced for  a  distance  of  700  feet  from  the  shaft  the  thickness  of  the 
masonry  was  increased  to  2y2  feet,  additional  strength  being  deemed 
necessary  because  of  the  greater  weight  to  which  it  would  be  sub- 
mitted after  the  removal  of  the  air-pressure ;  this,  of  course,  being 
due  to  the  increase  in  the  depth  of  water. 


44  TUNNELING   UNDER  THE   HUDSON   RIVER. 

For  each  foot  of  tunnel  about  14  cubic  yards  of  silt  were  exca- 
vated— one-half  of  this  being  taken  out  and  disposed  of  as  hereto- 
fore described,  and  the  remainder  being  thrown  back  into  the  fin- 
ished work.  Each  running  foot  of  tunnel  contained  over  132  cubic 
feet  of  masonry,  about  3,000  bricks,  6  barrels  of  cement,  and  10 
barrels  of  sand. 

By  the  aid  of  the  pilot  the  grade  of  the  tunnel  could  be  kept 
almost  absolutely  true,  and  any  trilling  variations  that  might  occur 
could  be  readily  rectified  during  the  advance.  It  was  preferably 
located  at  a  point  a  little  above  the  axis  of  the  tunnel ;  and  although 
this  rule  was  by  no  means  rigidly  followed,  experience  proved  that 
that  was  the  best  position  to  insure  rapid  work  of  good  character 
prosecuted  without  risk.  This  left  a  hirge  space  under  the  pilot  in 
which  to  move  the  excavated  material  from  the  heading,  and  did  not 
take  from  its  usefulness  as  a  foundation  for  the  braces,  which,  by  this 
arrangement,  could  be  more  easily  put  in,  since  the  shortest  ones  sup- 
ported the  roof-plates  and  the  longest  ones  the  plates  for  the  invert. 

During  all  these  operations,  in  fact  at  every  stage  of  the  work, 
a  constant  vigilance  was  enforced  to  detect  and  stop  leaks.  Air  es- 
caping through  a  minute  hole  made  no  audible  sound,  but  the  open- 
ing, unless  soon  stopped,  grew  larger  and  larger  with  great  rapidity. 
The  flow  through  a  single  hob'  was  insignificant,  but  when  these 
holes  were  closely  distributed  over  a  large  surface  the  quantity  of 
air  lost  became  of  importance.  Yet  this  care  was  not  exercised  with 
a  view  toward  saving  the  air  thus  lost.  The  atmosphere  in  a  cham- 
ber such  as  was  formed  at  the  heading,  and  in  which  many  men 
were  working,  soon  became  impure  unless  it  could  be  often  replaced 
by  fresh  air  ;  the  only  passages  through  which  the  vitiated  air  could 
pass  out  were  the  leaks  and  through  the  lock  placed  in  a  bulkhead 
in  the  tunnel,  as  we  shall  presently  describe.  The  principal  object, 
and  one  on  which  the  temporary  welfare  of  the  work  depended,  was 
to  prevent  the  escape-openings  from  assuming  such  proportions  as  to 
be  beyond  control,  since  in  that  case  a  blow-out  would  be  the  result 
and  the  tunnel  would  be  flooded.  This  inspection  extended  from 
the  uncovered  silt  at  the  heading  back  to  the  masonry,  and  em- 
braced every  spot  at  which  escape  of  air  was  possible.  Although 
men  were  appointed  to  perform  this  labor,  it  was  the  duty  of  each 
one  to  be  on  the  look-out. 


TUNNELING    UNDER  THE   HUDSON   RIVER.  45 

A  bulkhead  was  built  in  both  the  north  and  south  tunnels  at  a 
distance  of  430  feet  from  the  shaft.  This  step  was  necessary,  since 
the  leakage  through  the  long  line  of  brick-work  had  become  trouble- 
some, and  the  air-pressure  needed  to  keep  the  silt  in  place  at  the 
deepest  points  at  the  headings  too  great  to  be  safely  applied  to  the 
tunnels  at  their  highest  parts.  This  formed  two  independent  air- 
chambers  at  the  headings  of  the  tunnels.  The  bulkheads  were  brick 
walls,  4  feet  thick,  let  into  the  tunnels,  as  shown  in  the  longitu- 
dinal and  cross-sectional  drawing,  Plate  XY.  Each  wall  was 
backed  by  a  solid  wall  of  horizontally-placed  timbers  12  inches 
square,  against  which  rested  vertical  timbers,  which  were  strongly 
secured  by  braces  let  into  the  permanent  masonry.  Two  air-locks, 
15  feet  long  by  6  feet  in  diameter,  and  similar  in  general  plan 
to  the  first  air-lock  in  the  shaft,  were  put  in  each  bulkhead.  The 
construction  of  the  air-lock  is  very  clearly  shown  in  Plate  XVI. 
The  plates  were  bolted  together  in  order  that  the  lock  could  be 
taken  down,  transferred  to  a  more  advanced  bulkhead,  and  re- 
assembled. It  was  designed  that  one  of  these  locks  should  always 
be  open  toward  the  heading,  in  order  to  afford  a  jriace  of  refuge  for 
the  men  in  case  of  necessity  ;  the  second  lock  was  used  for  the  pas- 
sage of  supplies,  etc. 

After  the  completion  of  these  bulkheads  the  tunnels  between 
them  and  the  shaft  were  thrown  open  to  the  air.  It  may  be  well  to 
state  here  that  this  portion  of  the  work  has  been  open  for  very 
nearly  three  years,  and  has  shown  no  signs  of  displacement,  and  the 
masonry  is  as  perfect  as  when  first  built. 

No  attempt  was  made  to  connect  the  working-chamber  with  the 
shaft — cutting  through  the  west  side  of  the  caisson — until  the  bulk- 
heads had  been  put  in  ;  but  the  inconvenience  resulting  from  the 
necessity  of  taking  all  the  supplies  through  the  caisson-locks  com- 
pelled the  finishing  of  this  section  as  soon  as  possible.  While  this 
task  presented  none  of  the  obstacles  that  had  long  been  confidently 
anticipated,  it  was  sufficiently  troublesome  to  keep  up  a  lively  inte- 
rest in  the  minds  not  only  of  those  engaged  in  it,  but  also  of  all 
those  at  work  in  the  east  heading  of  the  north  tunnel,  700  feet 
distant. 

After  discussing  various  plans,  one  proposed  by  Mr.  S.  II.  Finch, 
assistant  engineer,  was  adopted.     This  plan  was  simply  to  close  the 


46  TUNNELING   UNDER  THE  HUDSON   RIVER. 

doors  of  the  old  air-lock  and  shafts  leading  to  the  tunnel,  admit  the 
compressed  air,  and  prosecute  the  work  in  the  same  way  as  at  the 
heading.  Preparations  were  made  by  sending  down  several  days' 
supply  of  brick,  sand,  broken  stone,  and  cement,  after  which  the 
doors  were  shut  and  the  pressure  raised  to  9  pounds  per  square 
inch.  The  lowest  section  of  the  material  through  which  the  work 
had  to  pass  was  sand,  the  middle  section  was  silt,  and  the  upper  silt 
and  cinders.  These  had  been  undisturbed  for  several  months,  and, 
it  was  thought,  had  become  compact  enough  to  permit  work.  It  will 
be  remembered  that  the  caisson  was  about  3  feet  less  in  length  than 
the  shortest  distance  between  the  shaft  and  tunnels,  and  at  the  sides 
of  the  shaft  about  15  feet  less,  so  that  the  connecting  tunnels  were 
wedge-shape  in  plan,  one  side  being  curved  to  conform  to  the  con- 
tour of  the  shaft. 

The  false  brick-work  which  had  been  put  in  to  enclose  the  cais- 
son was  taken  out,  as  were  also  the  timbers  on  that  side  of  the  cais- 
son. The  material  was  found  to  be  quite  dry  and  very  compact, 
although  it  was  a  mixture  of  ashes  and  silt  in  about  equal  parts. 
No  trouble  was  experienced  in  placing  the  roof-plates,  and  the  work 
proceeded  rapidly,  but  with  extreme  caution.  After  the  excavation 
had  been  made,  the  iron  shell  and  a  portion  of  the  invert  of  the 
south  connections  put  in,  and  when  the  silt  had  been  removed  in  the 
north  connection  to  within  about  3  feet  of  the  bottom,  the  water 
came  in  so  quickly  as  to  compel  a  cessation  of  work.  A  2-inch 
blow-out  being  of  no  use,  the  pump  in  the  shaft  was  connected 
with  the  stand-pipe  and  the  full  head  of  steam  turned  on,  while  the 
air-pressure  was  increased  to  11  pounds  per  square  inch,  when  the 
water  suddenly  disappeared.  The  remaining  silt  was  then  removed, 
but  before  the  plates  could  be  connected  at  the  bottom  the  water 
again  rushed  in,  but  receded  with  the  tide,  leaving  the  bottom  dry, 
when  the  masonry  was  laid  without  further  trouble.  Afterward  the 
false  piece  in  the  shaft  was  taken  out,  thereby  completing  the  work. 
Both  the  filling  and  sand  through  which  the  connecting  tunnels 
were  carried  contained  abundance  of  water,  and,  the  east  heading 
being  the  lower,  it  was  feared,  in  the  event  of  water  breaking  in  freely, 
that  the  air-locks  leading  to  that  heading  might  become  submerged, 
and  thus  close  the  only  avenue  of  escape  of  some  forty  men  who 
were  engaged  in  pushing  forward  toward  the  middle  of  the  river. 


Plate   XVII. 


Plate    XV. 


lil^lllSSI 


LONGITUDINAL   AND   CROSS   SECTION    THROUGH    BULKHEAD   IN    TUNNEL. 


CROSS  SECTION  AT  END 


HORIZONTAL  AIR  LOCK-  MADE  IN  SECTIONS  TO  FACILITATE  MOVING  TO  FRONT 


LONGITUDINAL  SECTION   AND  PLAN   SHOWING  TUNNELS  AS  CONNECTED  WITH    I  HE  SHAFT. 


Plate  XVI. 


.IVX    9tJ5iq 


. 


TUNNELING   UNDEK  THE   HUDSON   RIVER.  47 

During  the  entire  time  those  men  were  not  interrupted  for  one  mo- 
ment. Plate  XVII.  shows  the  tunnels  as  finally  and  permanently 
connected  with  the  shaft. 

A  platform  had  been  built  in  the  shaft  at  a  height  of  about  two- 
thirds  that  of  the  tunnels  ;  this  was  the  general  distributing  point 
for  material  passing  either  way.  A  single  track  led  from  the  shaft 
to  each  tunnel,  where  it  met  the  double  track  extending  down  to  the 
locks.  An  elevator  was  located  just  east  of  the  centre  of  the  shaft ; 
cms  loaded  with  supplies  were  run  upon  the  cage,  which  was  then 
lowered  to  the  platform,  where  they  were  run  upon  the  track  leading 
to  the  lock  in  the  bulkhead,  through  which  they  were  passed  to  the 
heading.  Each  car  was  provided  with  a  brake  with  which  to  govern 
its  speed,  the  descent  being  made  by  gravity.  As  the  cars  were 
brought  up  the  tunnel  they  were  run  upon  the  elevator,  raised  to  the 
surface,  and  run  upon  a  track  leading  to  the  low  lands  ;  by  this  plan 
the  silt  was  handled  but  once,  and  much  time  and  labor  were  saved. 

In  the  north  tunnel,  at  a  distance  of  280  feet  from  the  first  bulk- 
head, a  second  one  was  built  similar  to  the  first,  with  the  exception 
that  it  contained  but  one  air-lock,  which  was  deemed  sufficient, 
since  the  air-pressure  in  the  chamber  between  the  two  bulkheads 
was  kept  at  but  a  few  pounds — an  average  of  about  6 — less  than 
that  required  at  the  heading. 

Material  Was  drawn  from  the  heading  to  the  second  lock  and 
thence  to  the  first  by  a  horse  and  a  mule.  These  animals  had  with 
great  difficulty  been  taken  through  the  air-lock,  and  had  remained 
under  pressure  varying  from  20  to  33  pounds  per  square  inch  for 
several  months  without  showing  any  signs  of  suffering  ;  in  fact,  the 
horse  when  introduced  was  almost  useless,  since  he  was  old  and  se- 
verely afflicted  with  the  heaves,  but  while  in  the  tunnel  he  improved 
much,  having  been  cured  of  the  heaves  and  having  gained  in  flesh, 
although  almost  continually  at  work.  Upon  their  removal,  which 
was  made  necessary  by  the  cessation  of  operations,  the  mule,  which 
had  been  under  pressure  about  three  months,  was  liberally  dosed 
with  ergot,  whiskey  and  ginger,  and  in  a  few  hours  was  as  well  as 
ever.  But  not  so  with  the  old  horse,  that  had  been  in  seven  months. 
He  was  subjected  to  the  same  treatment,  but  the  change  had  been 
made  too  suddenly  (he  was  taken  out  in  about  half  an  hour),  for  in 
a  few  minutes  he  was  dead. 


48  TUNNELING  UNDER  THE  HUDSON   RIVER. 

In  November,  1882,  work  on  the  New  Jersey  side  was  stopped  be- 
cause of  lack  of  funds.  This  was  greatly  to  be  regretted,  as  the 
work  was  progressing  very  rapidly  and  to  the  complete  satisfaction 
of  all  interested.  During  the  last  four  weeks  127  feet  of  finished 
tunnel  had  been  put  in  ;  this  was  an  average  of  4^  feet  each  day. 
Had  operations  continued,  in  all  probability  the  north  tunnel  would 
have  been  completed  six  months  since.  The  north  tunnel  had 
been  built  for  a  distance  of  1,550  feet  from  the  sliaft  and  the 
south  tunnel  for  570  feet.  The  headings  were  securely  bulkheaded, 
and  for  some  time  the  finished  sections  were  kept  free  of  water ; 
but,  as  the  exact  date  of  resumption  could  not  be  determined,  it  was 
thought  best  to  devote  all  the  energies  to  pushing  forward  the  work 
from  the  New  York  side.  Consequently  the  pumps  were  stopped, 
when  the  water  very  slowly  found  its  way  into  the  tunnels  from  leaks 
around  the  shaft,  flooding  the  whole  in  about  three  months  ;  this  is 
the  condition  of  the  undertaking  at  the  present  writing  (December, 
1884). 

Before  the  water  was  permitted  an  entrance  the  bulkheads  in  the 
tunnels  were  so  firmly  strengthened  that  their  giving  away,  or  be- 
coming weakened  from  any  cause,  was  rendered  impossible.  The 
pumping  machinery  is  so  disposed  that  it  can  be  set  in  operation  at 
a  moment's  notice,  and  it  is  powerful  enough  to  relieve  the  tunnel 
of  water  in  two  or  three  days. 


CHAPTER  VII. 


SILT,  ANALYSIS  AND  PHYSICAL  PROPERTIES — ITS  RESISTANCE  TO 
DISPLACEMENT — EFFECT  OF  OOMPRESSED-AIR  UPON  SILT — DET, 
MOIST,  AND  SATURATED  SILT — THE  USE  OF  COMPRESSED-AIR — 
STOPPING  LEAKS — EFFECT  OF  OOMPRE8SED-AIR  UPON  THE  MEN-, 
AND   SENSATIONS   IN    PASSING  THROUGH   THE   AIR-LOCK. 

It  is  extremely  doubtful  if  a  substance  could  be  found  which 
would  be  better  adapted  to  submarine  tunneling  by  compressed  air 
than  the  so-called  silt  that  constitutes  tlie  bed  of  the  Hudson  River. 
As  there  found  it  is  of  very  uniform  character,  extends  entirely 
across  the  river,  and  is  of  sufficient  depth  to  wholly  surround  the 
tunnel,  except  for  a  distance  of  about  900  feet  on  the  New  York  side, 
where,  in  places,  it  will  cover  but  about  two  thirds  of  the  structure, 
leaving  from  2  to  7  feet  of  the  lower  side  embedded  in  sand  or  rock. 

It  is  a  washing  brought  by  the  water  from  the  upper  regions 
drained  by  the  river,  and  the  magnitude  of  the  deposit,  in  the  area 
covered  and  depth  (varying  from  28  to  100  feet),  indicates  that  the 
work  has  been  going  on  for  ages. 

An  analysis  made  by  A.  R.  Leeds,  Professor  of  Chemistry  at 


btevens  Institute,  gave  trie  iol 

Combined  water, 
"         silica, 

lowing 

result : 

Per  cent. 

5.13 

58.95 

Free  silica,  or  quartz,  . 
Alumina, 

10.32 
15.14 

Protoxide  of  manganese, 

0.95 

"              iron, 

3.28 

Sesquioxide  of  iron, 
Lime, 

1.38 
2.88 

Magnesia, 

Sodium  combined  as  chloride, 

1.50 
0.23 

Chlorine  existing  in  form  of  chloride, 

0.38 

Sulphuric  acid, 
Titanic         " 

i 

49 

trace, 
trace. 

50  TUNNELING   UNDER  THE   HUDSON   RIVER. 

Silt  is  of  a  dark  slate-color,  has  very  slight  cohesive  properties 
when  dry — it  may  be  easily  crumbled  in  the  hand — is  in  the  form  of 
an  impalpable  powder,  is  very  sparingly  mixed  with  hard,  rocky 
substances  which,  when  they  do  occur,  bear  a  close  resemblance  to, 
and  in  some  cases  are,  petrifactions  of  wood.  Shells  of  a  small  size 
are  not  infrequently  found  in  it,  but  gravel-stones  and  small  boul- 
ders are  seldom  encountered.  When  it  carries  the  proper  degree  of 
moisture  it  forms  a  compact,  dense,  tenacious  mass,  having  a  most 
effective  power  of  cohesion  that  enables  it  to  retain  a  given  shape 
for  an  extended  period  of  time  ;  in  this  state  it  may  be  handled 
much  as  ordinary  putty  can,  and  which  it  very  closely  resembles 
both  in  feeling  and  in  the  after-effect  produced  upon  the  hands.  It 
is  not  dirty,  in  the  usual  sense  of  this  word  ;  a  little  water  quickly 
relieves  the  hands  of  its  presence,  and  the  flesh  has  a  soft,  almost 
oily,  feeling  afterward.  The  most  important  feature  in  its  relation  to 
the  work  we  are  describing,  and  one  directly  the  outcome  of  its  cohe- 
siveness  when  of  the  proper  degree  of  saturation,  is  that  both  air 
and  water  pass  through  ifveiy  slowly.  When  well  mixed  with  a 
sufficient  volume  of  water  it  flows  as  freely  as  quicksand  and  is 
much  more  difficult  to  control. 

In  a  paper  read  by  General  William  Sooy  Smith  before  the 
Western  Society  of  Engineers  we  find  the  following  paragraph: 
" 'When  exposed  to  air-pressure  of  20  pounds  to  the  square  inch 
it  requires  an  additional  pressure  of  2,700  pounds  to  the  square 
foot  to  force  a  disk  into  it,  this  pressure  being  accompanied  by 
vibration.  Its  total  resistance  to  displacement  at  a  depth  of  Go  feet 
below  water-surface  (at  which  depth  experiments  were  made  to  de- 
termine this  resistance)  would  therefore  seem  to  be  5,680  pounds  per 
square  foot.  This  is  relied  upon  to  insure  permanency  of  the  work 
under  the  conditions  of  actual  use.  It  is  easy  to  make  a  cut  into  it 
2^  by  5  feet,  and  5  feet  deep,  in  order  to  place  in  position  one  of  the 
plates  of  the  iron  shell." 

It  was  impossible  to  force  the  hand,  either  clenched  or  open,  to 
any  considerable  depth  into  the  silt  at  the  exposed  heading  of  the 
tunnel ;  and  when  the  surface  was  struck  a  heavy  blow  with  the  fist 
a  dull  sound  was  produced,  and  hardly  any  depression  was  formed 
beyond  the  mere  imprint.  The  steps  into  which  the  heading  was 
cut  retained  their  sharp  outlines  amply  long  enough  to  enable  the 


TUNNELING    CINDER   THE    BUDBON    i:iVrER.  51 

men  to  place  the  plates  in  the  upper  portion  of  a  ring  and  excavate 
a  new  scries  of  Steps.  It  is  impossible  for  moist  silt,  because  of  its 
very  nature,  to  permit  an  air  pocket  to  remain  in  it.  This  was 
clearly  indicated,  by  the  settling  which  took  place  when  spaces  were 
left  between  the  crown-plates  and  the  undisturbed  sill,  and  when 
the  south  tunnel  upon  the  New  Jersey  side  was  started  by  being 
built  around  a  core  of  silt.  The  settlement  took  place  gradually, 
slowly,  evenly  and  surely  ;  the  rate  of  any  settling  movement  al- 
ways seemed  to  depend  directly  upon  the  amount  of  water  distri- 
buted in  the  silt  through  mechanical  disturbance — when  the  water 
was  largely  in  excess  the  silt  flowed  in  a  stream  ;  when  compara- 
tively dry  it  crumbled,  and  huge  pieces  would  fall. 

Compressed  air  affected  the  silt  by  driving  the  water  back  in  it; 
the  distance  to  which  the  water  was  forced,  and  what  we  might  term 
the  thoroughness  with  which  this  operation  was  performed,  depend- 
ed upon  the  ratio  existing  between  the  amount  of  air-pressure  and 
the  hydrostatic  head.  As  we  have  previously  mentioned,  it  was  not 
essential  to  maintain  an  air-pressure  in  the  work  equal  to,  or  in  ex- 
cess of,  the  water-pressure  in  order  to  accomplish  the  best  results  ; 
the  air-pressure  was  almost  invariably  kept  a  little  less  than  the 
water-pressure.  This  slight  difference,  which  was  seemingly  re- 
versed, varied  according  to  the  density,  or  compactness,  of  the  silt 
worked  through,  and  consequently  it  fluctuated  from  one  extreme 
to  the  other.  Of  course  the  distance  to  which  the  air  penetrated 
in  the  silt,  pushing  the  water  before  it,  was  influenced  by  the  amount 
of  pressure — an  air-pressnre  but  one  pound  lower  than  the  water- 
pressure  forced  the  water  out  more  rapidly  and  dried  the  silt  to  a 
greater  depth  than  an  air-pressure  of  5  pounds  less.  Therefore  the 
only  method,  having  absolute  reliability,  of  determining  the  proper 
air-pressure  was  to  vigilantly  and  continually  watch  the  exposed  silt 
in  the  heading.  A  smooth,  even,  and,  in  a  certain  way,  a  glossy  sur- 
face, when  rubbed  with  a  shovel  or  with  the  hand,  indicated  that  the 
silt  and  water  were  mingled  in  correct  proportion.  A  tendency  to- 
ward hurtful  dryness  was  first  shown  by  the  appearance  of  small, 
pin-like  apertures  through  which  the  air  might,  or  might  not,  be 
escaping  ;  this  was  remedied  by  decreasing  the  air-pressure.  A  wet, 
clammy  surface,  down  which  the  water  trickled,  showed  that  the 
water  was  in  the   ascendency  and  should   be   forced  back  by  an 


52  TUNNELING    UXDER   THE  HUDSON   RIVER. 

increased  air-pressure.  These  might  be  said  to  embrace  the  scale 
of  variations  beyond  which  it  was  dangerous  to  go  either  way  ;  the 
drying  process  might  continue  until  a  great  mass  of  silt  became 
detached,  thereby  opening  so  large  a  passage  for  the  air  to  escape 
through  as  to  be  beyond  control ;  or  the  silt  might  become  so 
thoroughly  saturated  with  water  as  to  flow  in  in  a  large  stream. 
The  air  within  the  tunnel  was  very  moist,  and  the  warmth — the 
temperature  was  about  75  degrees— caused  a  condensation  upon  the 
cold  surface — normally  about  55  degrees — of  the  freshly-exposed 
silt,  which  was  often  mistaken  for  water  coming  in  through  the  silt ; 
a  little  excess  of  pressure  would  force  this  water  back  and  thus 
cause  a  dry  surface. 

A  most  important  fact  may  be  here  noted  :  to  effect  these 
changes  required  considerable  time,  and  by  the  exercise  of  ordinary 
caution  could  always  be  detected  in  season  to  prevent  mischief.  It 
was  not  possible  to  instantly  dry  or  instantly  saturate  the  silt. 
This  feature  guaranteed  the  safety  of  the  men  and  work,  unless  the 
former,  owing  to  long-continued  immunity  from  anything  even  re- 
motely resembling  a  blow-out,  should  become  careless  and  neglect 
measures  tending  to  their  own  welfare. 

Silt,  as  found  in  its  natural  position,  was  practically  impervious  to 
both  air  and  water.  This  feature  was  clearly  shown  when  it  took  the 
air  four  days  to  pass  through  8  feet  of  sill  next  to  the  shaft,  the  air- 
pressure  being  2  pounds  greater  than  the  hydrostatic  head.  A  cup 
made  of  silt,  one  inch  thick,  would  hold  water  for  several  days  if  not 
disturbed,  but  a  very  slight  jar  would  greatly  change  its  character. 

The  air-pressure  served  as  a  support  for  the  plates  which  not 
only  acted  as  an  additional  guard  to  confine  the  air,  but  which 
possessed,  when  in  the  form  of  a  completed  ring,  great  strength  to 
resist  external  strain  ;  they  also  served  to  distribute  the  load  more 
evenly.  The  four  angle-irons  riveted  to  each  plate,  and  the  method 
of  uniting  them,  increased  their  capability  to  wit  list  and  bending, 
and  most  materially  stiffened  the  shell  as  a  whole.  In  the  sand 
upon  the  New  York  side  the  plates  alone  confined  the  air,  the  sand 
offering  no  resistance  to  its  passage.  If  the  shell,  then,  had  been 
dependent  solely  upon  braces  for  support— the  balancing  air-pres- 
sure all  being  removed — it  would  have;  been  absolutely  impossible 
to  have  made  any  advance  whatever. 


TUNNELING   UNDER  THE    HUDSON    RIVER.  63 

Small,  incipient  leaks  in  silt  were  stopped  by  application  of  wet 

silt  ;  in  openings  demanding  stronger  treatment  bags  of  cement  were 
sometimes  inserted.  The  air  rushing  through  a  hole  would  catch 
and  hold  the  material  placed  in  that  hole.  (The  writer  is  well  aware 
that  this  feature  of  tunneling  by  compressed  air  has  been  much  dis- 
puted, but  it  is  nevertheless  true,  and  it  has  been  done  so  many 
times  that  it  cannot  be  controverted.)  A  disk  of  paper  or  a  piece  of 
leather  held  at  the  hole  would  be  sustained  by  the  air.  The  tem- 
porary closing  of  the  opening  was  oftentimes  sufficient  to  prevent 
further  escape.  The  explanation  is  simple  :  as  soon  as  the  opening 
had  been  closed,  the  silt,  through  which  the  air  had  forced  and 
kept  open  a  channel,  settled  back  to  its  original  position,  and  the 
compactness  of  this  portion  depended  upon  the  time  during  which 
the  silt  was  allowed  to  settle.  This  was  illustrated  at  one  time  very 
forcibly  by  Mr.  Anderson,  while  working  under  the  dock  at  the 
New  Jersey  side,  thrusting  his  shoulders  into  a  hole  which  was 
quickly  assuming  dangerous  proportions.  By  working  his  shoul- 
ders and  forcing  them  up  he  was  soon  enabled  to  "fit"  himself 
into  the  aperture — the  instant  at  which  the  fit  was  accomplished 
being  indicated  by  the  pressure  catching  and  holding  him.  The 
silt  fell  back  and  in  a  short  time  was  dense  enough  to  admit  of 
the  usual  method — forcing  in  silt — being  carried  out. 

That  the  men  stood  the  compressed  air  so  well  was  in  a  great 
measure  due  to  the  admirable  precautions  and  regulations  of  the 
company.  Each  man  was  examined  by  a  physician  before  he  was 
allowed  to  enter  the  work,  and  all  not  in  robust  health,  particu- 
larly those  suffering  from  lung  or  heart  trouble,  were  rejected. 
The  first  time  a  man  passed  through  the  lock  the  pressure  was  ad- 
mitted very  slowly  and  the  effect  upon  him  carefully  noted.  He 
was  told  how  to  relieve  the  unpleasant  ear  effect,  and  if  there  was 
no  further  trouble  he  was  introduced  to  the  heading.  A  person 
being  subjected  to  gradually  increasing  air-pressure  experiences  a 
hard  pressure  upon  the  interior  of  the  ears,  accompanied  by  more 
or  less  pain.  Coughing,  violently  blowing  the  nose,  swallowing, 
etc.,  will  relieve  it  for  the  time  being,  but  as  the  pressure  increases 
it  returns,  wdien  swallowing  is  again  resorted  to.  As  the  men 
emerged  from  the  tunnel  all  violent  exercise  was  forbidden  ;  but  as 
some  of  the  stronger  ones  would  run  up  the  stairs  in  the  shaft  (New 


54  TUNNELING  UNDER  THE   HUDSON   RIVER. 

Jersey  side),  a  rule  was  laid  down  that  all  should  be  taken  up  on 
the  elevator.  Upon  the  New  York  side,  the  air-lock  being  at  the 
top  of  the  shaft  and  near  the  surface,  no  climbing  was  necessary 
after  coming  out. 

The  effect  produced  by  entering  compressed  air  is  to  start  a 
profuse  perspiration,  to  increase  the  heart-beats  but  make  them 
weaker,  and  to  exhilarate  the  individual.  The  sense  of  smell  is  so 
weakened  as  to  only  detect  the  most  powerful  odors,  or  is  com- 
pletely annulled  ;  the  other  senses  seem  to  be  unaffected.  Upon 
leaving  compressed  air  a  person  feels  weakened  for  a  time  and  is 
averse  to  exertion  ;  this  soon  passes  away.  Men  laboring  in  an 
air-pressure  need  more  sleep  and  sleep  sounder  than  those  working 
in  the  open  air.  Compressed  air  should  neither  be  entered  with  a 
full  nor  an  empty  stomach  ;  an  hour  or  two  after  the  meal  is  the 
best  time.  The  use  of  liquors  was  prohibited  (unfortunately  there 
was  no  way  of  enforcing  this  rule) ;  strong  coffee  was  given  the  men 
as  they  came  from  the  lock. 

There  were  comparatively  few  cases  of  caisson  disease,  none  of 
which  was  fatal.  The  suffering  was  mainly  confined  to  the  limbs, 
the  body  being  but  infrequently  affected.  Upon  the  New  Jersey  side 
the  use  of  two  air-locks,  placed  two  or  three  hundred  feet  apart, 
lessened  the  danger  of  being  afflicted  with  this  disease,  sometimes 
designated  the  "bends."  After  passing  through  the  first  lock  a 
person  was  under  a  modeiate  pressure,  which  was  kept  at  about 
two-thirds  that  in  the  heading.  The  walk  from  this  lock  to  the 
second  accustomed  him  to  the  change,  and  he  was  less  affected 
when  passing  through  the  second.  The  highest  pressure  used  was 
34^  pounds  per  square  inch  (this  was  exceptional)  at  the  head- 
ing, that  between  the  locks  being  kept  at  about  ~2~>  pounds.  That 
continued  exposure  to  compressed  air  is  not  injurious  is  shown  by 
the  horse  and  mule  heretofore  mentioned,  which  not  only  lived  for 
months  in  the  tunnel,  but  kept  in  good  condition  and  worked  hard 
almost  constantly  day  and  night. 


CHAPTER  VIII. 

PLANS  FOR  BEACHING  GRADE  OF  TUNNELS  AT  NEW  YORK  SIDE — 
SHAFT  OR  CAISSON — DESCRIPTION  OF  CAISSON — AIR-LOCKS — ITS 
LOCATION — METHOD  OF  SINKING — PLANS  FOR  STARTING  TUNNELS 
— CUTTING  THROUGH  SIDE  OF  CAISSON — IRON  BULKHEAD — SIZES 
OF  PLATES — METHOD  OF  BUILDING  THE  TUNNEL — BULKHEAD  IN 
TUNNEL— HANDLING  MATERIAL — SAND-PUMP — BLOW-OUT — PILES 
MET — WORK  STOPPED — BOILERS  AND  AIR-COMPRESSORS — MATE- 
RIAL   REQUIRED   TO   COMPLETE   TUNNELS. 

In  this,  as  in  other  great  works  characterized  by  the  marked 
originality  of  the  plans  pursued,  experience  has  been  the  best 
teacher  and  most  trustworthy  guide.  When  selecting  methods  for 
accomplishing  a  certain  object  no  set  rule  applicable  in  all  cases 
could  be  deduced.  The  governing  conditions  changed  continually, 
and  it  was  impossible  to  calculate  the  direction  of  those  changes  ; 
the  time  at  which  features  compelling  modifications  in  the  plans 
would  present  themselves  was  always  an  unknown  factor.  We 
find  that,  before  the  exact  nature  of  the  material  constituting  the 
bed  of  the  river  had  been  ascertained,  the  shaft  seemed  to  offer  by 
far  the  cheapest,  quickest  and  safest  means  of  reaching  the  re- 
quisite depth  at  which  to  start  the  tunnels  ;  and,  as  this  had  worked 
well  on  the  New  Jersey  side,  plans  were  made  for  a  brick  shaft  by 
the  aid  of  which  to  reach  the  grade  of  the  tunnels  at  the  New  York 
end.  This  was  to  have  been  similar  in  form  to  the  first  one  and  42 
feet  inside  diameter,  but  in  addition  it  was  to  have  had  an  iron  shoe 
and  shell  outside  extending  up  35  feet  from  the  bottom,  and  so 
arranged  that  the  lower  25  feet  could  be  converted  into  a  caisson  by 
putting  on  a  diaphragm  or  roof.  It  was  designed  to  remove  this 
roof  after  the  tunnels  had  been  started  and  the  bulkheads  and  air- 
locks put  in. 

There  was  much  discussion  whether  to  adopt  this  plan  or  simply 
a  caisson  built  of  wood,  and,  as  usual  in  such  cases,  each  plan  had 
many  advocates.     The  timber  caisson  was  finally  decided  upon  as 

55 


56  TUNNELING   UNDEB  THE   HUDSON   RIVER. 

being  the  better,  although  experience  had  shown  that  it  caused 
much  inconvenience  in  getting  material  out  and  in.  It  was  also 
arranged  to  cut  a  shaft  through  the  roof  of  the  caisson  as  soon  as 
the  tunnels  had  been  extended  far  enough  to  permit  of  the  placing 
of  the  air-locks  ;  this  would  convert  the  caisson  into  a  spacious  and 
convenient  working-chamber.  There  can  be  no  question  as  to  the 
advantages  to  be  derived  from  a  large,  roomy  working-chamber  at 
the  entrance  to  the  tunnels  to  serve  as  a  centre  from  which  to  dis- 
tribute supplies  and  material. 

Work  upon  the  caisson  shown  in  Plate  XIX.  was  begun  in  July, 
1881.  The  bottom  was  48  feet  long  and  29 1/2  feet  wide ;  it  was  25 
feet  high,  and  the  sides  had  a  batter  of  one-half  to  one  and  were 
3  feet  thick.  The  top  was  46  feet  long  and  27^  feet  wide.  The 
transverse  struts  were  16  by  18  inches  ;  the  longitudinal  ones  Mere 
20  by  20  inches ;  the  vertical  ones  16  by  18  inches.  Transverse 
and  longitudinal  tie-rods  provided  with  turn-buckles  extended 
through  the  structure  from  outside  to  outside.  The  lower  edges 
of  the  sides  were'  bevelled,  and  shod  with  iron  to  form  a  cutting 
surface  that  would  resist  wear. 

It  will  be  seen  that  this  caisson  resembled  the  one  used  at  the 
other  side  of  the  river  only  in  the  form  of  its  exterior.  It  was  a 
much  more  difficult  structure  to  make  secure — the  heavy  timber  arch 
in  the  other,  together  with  the  triangular  sections  that  were  filled 
with  concrete,  greatly  increased  the  strength — and  the  shape  of  its 
interior  was  not  so  well  adapted  to  subsequent  operations.  In  ad- 
dition to  this  it  cost  much  more  to  build. 

Practice  upon  the  other  side  had  suggested  many  improvements 
in  the  number  and  disposition  of  the  air-locks,  and  extending 
through  the  roof  of  the  caisson  were  three  shafts  provided  with 
air-locks.  In  the  centre  of  the  roof  was  a  shaft  5  feet  in  diameter, 
to  the  lower  end  of  which  was  attached  a  cross-piece  6  feet  in  diame- 
ter and  15  feet  long.  At  each  end  of  the  cross-piece  was  a  door  3 
feet  wide  by  4  feet  high,  and  at  the  lower  end  of  the  shaft  was  a 
third  door.  Of  course  all  these  doors  opened  toward  the  interior, 
or  air-pressure,  and  when  closed  the  joints  were  made  air-tight 
by  means  of  rubber  packing.  This  shaft  extended  but  a  few  feet 
above  the  caisson  ;  a  wooden  box  slightly  flaring  toward  the  top 
extended  to  the  surface  of  the  ground.     At  one  side  of  this  shaft 


TUNNELING    UNDEB  THE    BUDS0S    BIVEE.  67 

was  a  second  one,  3  feet  in  diameter  and  extending  just  ill  rough 
the  roof,  and  furnished  with  :i  door  at  each  end.  Upon  the  other 
side  was  a  third  shaft,  5  feet  in  diameter,  at  the  upper  end  of  which 
— about  L5  feet  below  the  surface  was  the  air-lock  used  upon 
the  New  Jersey  caisson,  which  we  have  already  described,  and 
which  is  illustrated  in  Plate  IX.  The  central  airlock  was  ased 
for  the  passage  of  general  supplies  and  excavated  material;  the 
smallest  shaft,  built  long-  and  narrow,  was  used  in  getting  in  tim- 
bers, which  it  would  admit  in  long  lengths  ;  the  third  air-lock 
was  for  the  men. 

The  caisson  was  located  so  that  the  side  next  the  river  was  69 
feet  from  the  bulkhead-wall.  It  will  be  remembered  that  the  de- 
scent of  the  caisson  upon  the  New  Jersey  side  wras  guided  and  con- 
trolled by  six  suspender-rods,  upon  which  screwed  nuts  resting 
upon  heavy  timbers  projecting  over  the  edge  of  the  coffer-dam  and 
extending  back  upon  the  ground,  the  rear  ends  being  held  down 
by  heavy  weights.  This  arrangement  was  considered  superfluous 
upon  the  New  York  side,  and  no  device  was  used  to  control  or  guide 
the  caisson  as  it  descended.  The  sides  Avere  extended  upward  to 
form  a  box  or  coffer-dam  which  contained  the  enormous  weight 
necessary  to  force  the  structure  down.  The  weight  of  load  was 
2,100  tons  and  of  caisson  400  tons,  a  total  of  2,500  tons.  A  pres- 
sure of  air  in  the  interior  prevented  the  water  from  rising  above  the 
line  of  the  shoes  or  lower  edge  ;  of  course  this  pressure  was  in- 
creased as  the  depth  became  greater. 

The  earth  was  carefully  removed  from  under  the  shoes,  and  the 
air-pressure — which  practically  formed  a  cushion  upon  which  the 
caisson  rested — lowered,  when  the  weight  overcame  the  friction  of 
the  earth  upon  the  sides  and  the  entire  structure  dropped.  These 
advances  were  made  through  only  short  distances  at  a  time,  and 
great  care  was  exercised  in  having  the  trench  under  the  shoe  per- 
fectly level  and  as  free  as  possible  from  large  stones,  in  order  to 
prevent  all  liability  of  straining  the  caisson  by  unequal  sinking. 
After  having  passed  through  loose  filling  and  dock-mud  the  lower 
edge  rested  in  sand  at  a  depth  of  62  feet  from  the  ground-surface 
and  3  feet  above  the  exterior  of  the  invert  of  the  tunnels.  The  top 
of  the  coffer-dam  was  cleaned  out  to  a  depth  of  about  15  feet,  and 
the  sides  were  firmly  secured  by  cross-braces,  and  a  platform  built. 


68  TUNNELING  UNDER  THE   HUDSON   RIVER. 

Through  the  centre  of  this  chamber  passed  the  wooden  shaft  lead- 
ing to  the  supply-lock.  The  timber-lock  reached  nearly  to  the 
platform,  and  the  air-lock  for  the  men  was  just  above  the  platform, 
from  which  a  ladder  led  to  the  surface. 

Almost  the  whole  of  the  caisson  was  in  sand,  and  the  two  tun- 
nels would  be  entirely  embedded  in  sand  and  gravel.  It  will  be 
seen  that  the  material  was  very  different  from  that  encountered 
at  the  other  side  of  the  river,  and  instead  of  facilitating  the  work  it 
proved  to  be — as  it  generally  is  in  undertakings  of  this  kind — one 
of  the  most  difficult  to  handle.  Some  parts  of  the  following  para- 
graph, published*  by  the  writer  after  both  tunnels  had  been  car- 
ried a  short  distance  from  the  caisson,  are  applicable  to  many 
stages  of  this  work,  which  has  been  most  freely  criticised  and  most 
sparingly  studied:  "The  fact  that  the  caisson  was  embedded  in 
sand  led  to  the  belief  among  many  engineers  of  high  standing  that 
an  outlet  could  not  be  obtained  and  the  tunnel  started  by  the  sys- 
tem of  working  by  compressed  air.  Indeed,  it  has  become  unsafe 
to  pronounce  an  unfavorable  opinion  in  regard  to  any  particular 
piece  of  work  connected  with  the  tunnel ;  in  more  than  one  in- 
stance obstacles  which  seemed  to  present  an  insurmountable  bar- 
rier to  all  future  progress  have  been  met,  conquered,  and  the  work 
has  gone  forward.  New  devices  and  plans  have  kept  pace  with  new 
difficulties.  At  a  first  glance  the  sand  above  mentioned  seemed  to 
contain  all  the  characteristics  requisite  for  a  first-class  insurmount- 
able obstacle.  Upon  the  least  reduction  of  the  air-pressure  this 
material  would  follow  the  water  into  the  caisson;  the  smallest 
opening  afforded  a  ready  passage.  The  water  and  sand  could  be 
kept  quiet  as  far  down  as  the  air-pressure  was  carried,  and  no 
further;  and  if  a  trench  were  dug  or  undertaken  the  upward  pres- 
sure, due  to  the  difference  between  the  air-pressure  and  head  of 
water,  or  depth  of  excavation,  would  fill  the  trench  with  sand  and 
water  about  as  fast  as  it  could  be  taken  out,  and  the  adjacent  ma- 
terial would  then  be  in  no  belter  condition  than  at  first." 

The  iron  plates  upon  which  the  masonry  was  to  rest  were  laid 
along  the  north  and  south  sides  of  the  caisson,  being  carried  down 
in  horizontal  rows  on  the  curve  desired  for  the  invert.  Each  plate 
was  braced  as  it  was  put  in,  and  the  pressure  was  kept  a  little  below 

*  Engineering  Xews,  Sept.  2,  1882. 


TUNNELING   UNDER  THE    HUDSON    RIVER.  59 

the  hydrostatic  bead,  or  about  25  pounds  per  square  inch.  Here 
again  the  system  of  iron  plates  with  angles  attached  was  found  to 
be  of  very  great  value.  After  this  iron  shell  had  been  finished  the 
brick-work  was  laid.  Thus  was  provided  a  working-chamber,  or 
base  of  operations,  similar  in  many  respects  to  the  one  at  the  other 
shore.  The  work  was  relieved  of  water  by  means  of  a  rotary  pump 
located  at  the  surface  and  connected  with  a  stand-pipe  leading  into 
the  caisson,  where  it  joined  three  pipes  extending  to  different  parts 
of  the  chamber. 

To  cut  through  the  side  of  the  caisson  and  build  the  first  section 
of  tunnel  was  now  the  difficult  task.  This  was  by  far  the  most  for- 
midable obstacle  which  the  engineers  had  had  to  surmount.  The  ma- 
terial being  sand  and  gravel,  it  was  known  that  the  method  used  so 
successfully  when  working  through  pure  silt  would  be  of  no  service 
here  unless  radically  altered.  It  was  determined  to  use  compressed 
air  to  counterbalance  the  exterior  pressure  of  sand  and  water  ;  but  as 
the  sand  possessed  no  self-sustaining  qualities — it  was  as  unstable, 
practically,  as  the  water  surrounding  it — it  became  essential  to  inter- 
pose a  sheathing  between  the  air-chamber  and  sand.  While  insert- 
ing the  separate  sections  composing  this  lining,  whether  they  were 
of  wood  or  iron  plates,  it  Avould  be  of  vital  importance  to  hold  back 
the  sand  temporarily ;  and  since  the  joints  could  not  be  made  per- 
fectly impervious  to  water  without  delaying  the  work  too  much, 
some  plan  would  have  to  be  devised  for  removing  that  which  would 
come  in.  The  stand-pipes  above  referred  to  were  expected  to  do 
this. 

One  plan  which  was  believed  would  give  the  best  results  was  to 
construct  a  movable  bulkhead  of  oak  plank,  hold  it  at  the  ends  by 
heading-props  and  braces  from  the  side  of  the  caisson  or  face  of  the 
completed  work,  as  the  case  might  be,  and  extend  it  from  about  G 
inches  above  the  invert  to  the  roof  or  crown-plates.  The  opening  at 
the  bottom  was  to  permit  the  water  to  flow  from  the  heading  and  be 
pumped  out.  It  was  expected  that  considerable  would  drain  away, 
and  that  the  surroundings  would  thereby  be  improved.  Advance 
was  to  be  made  in  this  way :  The  air-pressure  being  maintained  at 
about  \y2  pounds  per  square  inch  more  than  what  would  be  required 
to  keep  out  water  at  the  crown,  the  upper  plank  would  be  removed, 
enough  material  taken  out  to  admit  a  plate,  when  the  plank  would 


60  TUNNELING  UNDER  THE  HUDSON   EIVEE. 

be  moved  forward  and  supported  against  the  next  set  of  supports. 
The  adjoining  plank  would  then  be  advanced  in  the  same  manner, 
and  so  on  down  to  the  bottom. 

In  actual  practice  iron  plates  and  angles  were  substituted  for 
plank,  and  the  conclusion  was  afterward  arrived  at  that  no  progress 
could  have  been  made  if  this  had  not  been  done,  from  the  mere  fact 
that  a  bulkhead  of  iron  could  be  made  almost  perfectly  air-tight — a 
feature  not  possible  with  one  of  wood. 

The  actual  work  of  cutting  through  the  side  of  the  caisson  may- 
be described  as  follows  :  A  score,  or  mark  (shown  in  the  dotted  lines 
in  the  longitudinal  section,  Plate  XIX.),  had  been  made  on  the  inner 
side  of  the  caisson,  of  the  exact  form  and  size  of  the  tunnel,  at  the 
time  of  its  construction,  and  no  spikes  had  been  driven  within  6 
inches  of  this  mark.  After  the  invert  had  been  completed  men 
were  set  at  work  boring  with  2  and  2^-inch  angers  on  that  mark,  the 
air-pressure  being  kept  at  about  18  pounds.  As  soon  as  the  calk- 
ing course  of  4-inch  planking  had  been  pierced  the  air  escaped  in 
small  quantities  ;  but  after  the  augers  had  reached  the  diagonal 
planking  between  the  12  by  13-inch  timbers  the  air  rushed  out  with 
a  loud  noise.  This  was  stopped  by  blowing  dry  cement  into  the 
holes  whenever  the  leak  occurred.  This  blowing  consisted  in  hold- 
ing a  lot  of  loose  cement  near  the  aperture,  into  which  the  escaping 
air  would  carry  it.  Usually  two  or  three  quarts  were  sufficient,  but 
in  the  case  of  the  first  openings  as  many  barrels  were  used.  "Wooden 
plugs  were  also  provided,  and  a  number  inserted  in  the  holes  imme- 
diately after  the  removal  of  the  augers ;  but  the  cement  proved  con- 
venient and  was  generally  used.  The  boring  was  continued  until 
nearly  the  entire  circumference  had  been  penetrated,  when  the  work 
of  cutting  out  was  begun.  Owing  to  the  number  and  arrangement 
of  the  spikes,  dowels,  tenons,  etc.,  employed  to  fasten  each  piece 
of  timber,  this  was  a  labor  of  great  magnitude,  requiring  the  exercise 
of  patience  and  perseverance.  The  caisson  wall  was  3  feet  thick, 
of  yellow  pine,  and  as  solid  as  it  was  possible  to  make  it.  As  soon 
as  a  hole  had  been  made  large  enough  to  admit  it  a  plate  was  in- 
serted and  held  firmly  in  place  by  braces.  To  keep  the  exposed 
portion  from  flaking  and  falling  before  the  plate  could  be  j)laced  in 
position  planks  were  held  against  it. 

At  a  distance  of  12  feet  from  the  side  of  the  caisson  a  bulkhead 


Plate  XVIII, 


Plate    XIX. 


48'- 

'*Longitudm»l  S9ct.on»l  E|e. 


Trsnivo'se  S«c1i 


VIEW  OFCAISSON.-NEW  YORK  SIDE 


Plate  XX. 


SECTIONAL  ELEVATION  THROUGH  CAISSON  ANO  TUNNEL 


CROSS  SECTION  TUNNE'L-NEW  JERSEY  SIDE. 


..Mivx  ajfiiq 


. 


TUNNELING  UNDER  THE  HUDSON   KIVER.  61 

of  iron  plates  was  started  at  the  top  and  built  down.  A  system  of 
struts,  resting  against  the  caisson,  supported  this  bulkhead,  which 
was  put  up  in  regular  courses  of  15  inches  each,  the  plates  being 
4  feet  in  length,  except  those  for  the  ends  of  each  course,  which 
were  cut  to  correspond  with  the  section  of  tunnel  at  the  respective 
courses.  It  was  found  impossible  to  advance  a  ring  of  plates  of  the 
usual  width — 2yi  feet — so  they  were  changed  to  one  half  this  width, 
or  15  inches.  This  was  the  first  modification  or  change  worthy 
of  note  from  the  practice  on  the  New  Jersey  side,  and,  although  it 
necessitated  more  labor,  it  was  beneficial  because  of  the  increased 
number  of  angle-bars,  in  one  direction,  which  nearly  doubled  the 
strength.  The  proper  thickness  of  the  plates  was  a  subject  much 
discussed  at  the  time,  it  being  maintained  by  some  of  those  con- 
nected with  the  work  that  it  could  be  done  without  great  or  un- 
usual risk  with  plates  of  any  thickness  (those  used  were  %.  of  an 
inch),  and  that  those  in  use  were  sufficient,  and,  being  light  and 
easily  handled,  it  was  expected  to  hold  them  in  place  by  the  ex- 
ercise of  skill  and  judgment  in  bracing.  Before  the  heading  had 
been  far  advanced  it  was  found  expedient  to  further  reduce  the  size 
of  some  of  the  plates,  for  reasons  explained  a  little  further  on. 

The  method  of  building  the  tunnel  may  be  briefly  summed  up 
as  follows  :  A  chamber,  generally  10  feet  long  and  in  cross-section 
equal  to  the  exterior  of  the  tunnel,  23  feet,  was  lined  with  iron 
plates  which  had  been  inserted  one  at  a  time,  beginning  at  the 
crown  of  the  arch  and  extending  down  the  sides  and  heading  ;  the 
rear  end  of  this  chamber  opened  into  the  completed  work.  After 
having  been  thoroughly  cleaned  the  brick-work  was  laid.  The 
amount  of  care,  skill,  patience,  and  perseverance  which  were  ne- 
cessarily exercised  in  prosecuting  this  section  of  the  work  success- 
fully will  be  fully  comprehended  by  all  those  who  have  ever  had 
their  undertakings  hazarded  by  quicksand  G5  feet  under  water. 

The  operation  of  advancing  the  plates  to  form  the  shell  was  an 
easy  matter,  so  far  as  the  roof- plates  were  concerned — about  one- 
fourth  of  the  circumference — although  great  care  and  skill  were  re- 
quired. The  plan  was  to  drive  light  "poling"  strips,  of  ^  by  2 
inches  and  about  2  feet  long,  directly  in  front  of  the  last  plate  put 
in  ;  the  rear  ends  of  the  strips  were  pushed  up  above  and  then 
pulled  back  so  as  to  rest  on  the  plate  already  in  place.      This  pre- 


62  TUNNELING   UNDER  THE   HUDSON    RIVER. 

vented  the  material  from  falling  while  the  excavation  was  being 
made  ;  where  the  air  would  escape  too  much  a  plaster  of  silt,  put 
on  over  the  sand,  would  effectually  stop  it.  The  plate  was  put 
in,  bolted  to  the  one  already  in,  and  a  short  brace  put  up,  tem- 
porarily, to  prevent  settling  ;  but  it  was  found  that  the  mate- 
rial on  which  the  lower  end  of  the  brace  rested  was  insecure, 
and  systems  of  A-braces,  diagonals,  verticals  with  mud-sills,  etc., 
were  tried,  but  nothing  but  failure  resulted.  When  the  head- 
ing had  been  extended  about  12  feet  and  the  bulkhead  put  in, 
reaching  across  the  face  of  the  heading  from  side  to  side  and  down 
about  C  feet,  it  was  found  that  the  continued  settlement  of  the  roof 
had  reached  a  point  when  some  radical  change  in  the  method  must 
be  adopted  or  the  work  Avonld  be  stopped.  A  system  of  bracing 
was  devised  which  supported  the  roof  most  admirably.  A  piece 
of  timber  12  inches  square  and  about  10  feet  in  length  was  so  placed 
that  one  end  rested  against  the  outside  of  the  caisson  and  the  other 
extended  into  the  face  of  the  heading.  The  forward  end  was  sup- 
ported from  the  inside  of  the  caisson  by  two  iron  tie-rods,  \y2  inch 
in  diameter  and  provided  with  turn-buckles,  thus  forming  a  kind 
of  boom,  which,  it  was  expected,  would  sustain  a  load  of  from  50  to 
75  tons.  An  upper  member  was  added  to  this,  and  with  a  strut  or 
two  formed  a  sort  of  truss  closelv  resembling  a  bridge- truss.     This 

*  O  CD 

arrangement  constituted  the  principal  aid  in  completing  the  first 
section.  Plate  XX.  is  a  sectional  side  elevation  through  the  cais- 
son and  completed  tunnel ;  it  also  shows  very  clearly  the  construc- 
tion of  the  sides  of  the  caisson. 

The  finally  adopted  method  of  building  the  tunnel  through  sand 
will  be  understood  from  the  engravings,  Plate  XXII.,  the  upper 
view  showing  the  first  work  done  upon  a  new  section,  the  centre 
view  showing  the  excavation  about  one-half  finished,  and  the  lower 
view  representing  the  chamber  lined  with  iron  plates,  cleaned  and 
ready  for  the  masonry ;  the  respective  cross-sections  showing  the 
bracing  are  seen  in  the  side  views. 

The  upper  middle  plate  of  the  bulkhead  of  the  completed  section 
having  been  removed,  the  first  crown  plate  of  the  next  section  was 
put  in  and  bolted  to  the  finished  ring  ;  plates  were  then  put  at  each 
side  and  bolted.  The  crown-plates  were  extended  as  far  as  possible 
before  the  next  rows  of  plates  in  the  heading  were  removed.     The 


TUNNELING   UNDER  THE   HUDSON   KIVER.  63 

side  plates  at  the  crown  were  also  carried  down,  so  that  tlieir  lower 
edges  might  be  below  the  upper  edge  of  the  highest  row  in  the  bulk- 
head. Since,  owing  to  the  air-pressure,  the  water  could  not  rise 
above  the  edges  of  these  plates,  the  main  efforts  were  directed  to- 
ward rapidly  advancing  the  roof-plates,  in  order  to  reach  the  new 
bulkhead.  When  this  was  reachud  the  plates  that  had  been  taken 
from  the  rear  bulkhead  were  put  up.  This  formed  the  segment  of 
a  tube  the  circular  portion  of  which  was  iron  and  the  base  sand. 
Short,  thick  timbers  resting  upon  plates  sunk  a  little  distance  into 
the  sand  floor  supported  the  iron  sheathing.  When  the  excavation 
had  been  carried  far  enough  down  to  admit  them  horizontal  timbers 
were  used  as  foundations  for  the  short  braces ;  the  rear  ends  of  these 
timbers  were  sustained  by  pieces  placed  against  the  finished  tunnel, 
and  the  middle  and  forward  parts  by  uprights  on  plates  in  the  sand. 
The  plates  were  slowly  and  carefully  inserted,  all  digging  being 
done  with  extreme  caution.  The  excavated  material  was  removed 
to  the  caisson-chamber,  and  from  there  taken  to  the  surface  in  a 
manner  presently  to  be  described. 

To  make  the  joints  between  the  plates  as  nearly  air-tight  as  pos- 
sible was  much  more  essential  upon  this  side  than  it  had  been  upon 
the  other,  and  it  was  a  much  more  difficult  undertaking  owing  to 
the  total  want  of  self-sustaining  power  in  the  sand,  which,  being 
continually  saturated  with  water,  offered  but  slight  resistance  to 
the  passage  of  air.  Of  the  many  substances  experimented  with,  silt 
brought  from  the  New  Jersey  side  proved  most  effectual  in  stopping 
leaks.  This  was  plastered  freely  over  the  iron-work,  and  by  closely 
watching  its  surface  the  incipient  leak  could  be  easily  detected. 

To  insert  the  plates  in  the  roof  and  invert  was  comparatively 
easy,  but  at  the  middle  section  greater  caution  was  exercised.  In 
order  that  the  exposed  eartli  might  be  of  as  small  area  as  possible, 
the  side  and  bulkhead  plates  were  cut  much  smaller,  as  shown  in 
plates  XXIII.,  XXIV.,  and  XXV.  Plate  XXIV.  shows  a  ring  of 
plates  as  it  would  appear  if  rolled  out  flat,  and  the  following  plate 
shows  how  a  large  plate  was  cut  up,  and  also  gives  the  dimensions 
of  each. 

As  has  been  before  stated,  it  was  necessary  to  increase  the  air- 
pressure  as  the  plates  in  the  section  were  carried  down  ;  the  hy- 
drostatic head  and  air-pressure  were  kept  about  balanced.     A  pres- 


64  TUNNELING   UNDER  THE   HUDSON    RIVER. 

sure  of  from  25  to  28  pounds  per  square  inch  was  required  during 
the  building  of  the  invert. 

Building  bulkheads  in  the  tunnels  at  certain  distances  and  in- 
serting air-locks  had  proved  so  satisfactory  in  the  work  at  the 
other  side  of  the  river  that,  at  a  distance  of  30  feet  from  the  cais- 
son, a  lock  15  feet  long  and  6  feet  in  diameter  was  built  upon  a 
bulkhead  of  concrete  6  feet  thick.  From  the  bulkhead  to  the 
arch  of  the  tunnel,  and  surrounding  the  lock,  Avas  a  wall  of  brick 
masonry  3  feet  thick.  This  lock  was  similar  in  construction  to 
those  which  we  have  described.  The  principal  details  and  loca- 
tion of  the  bulkhead  and  lock  will  be  readily  understood  from  the 
engravings,  Plate  XXYI. 

The  experience  gained  in  removing  the  excavated  material  from 
the  work  upon  the  New  Jersey  side  caused  many  changes  to  be  made 
in  the  construction  and  location  of  the  air-locks  in  the  working- 
chamber  of  the  New  York  caisson.  The  general  supply  lock,  pre- 
viously described,  had  a  horizontal  section  across  its  lower  end,  and 
the  shaft  leading  to  it  was  of  ample  size  to  admit  the  largest  pieces 
of  iron  entering  the  tunnel.  At  each  end  of  the  cross-piece  was  a 
door,  and  at  the  junction  of  the  shaft  and  cross-piece  was  a  third 
door  ;  the  shafl  was  always  open  to  the  air.  The  two  lower  doors 
being  closed,  the  brick,  sand,  cement,  plates,  etc.,  were  lowered 
down  the  shaft  by  means  of  a  block  and  tackle  attached  to  a  frame 
under  an  open  shed  built  over  the  opening.  When  the  air-lock  had 
been  filled  the  middle  door  was  closed,  and  after  the  air-pressure  in 
the  lock  equalled  that  in  the  working-chamber  the  end  doors  were 
thrown  open  and  the  load  removed.  Material  to  be  taken  out  was 
placed  in  the  lock,  and  from  there  raised  to  the  surface  by  a  hoist- 
ing-engine ;  it  was  then  carried  in  wheelbarrows  on  board  a  scow 
moored  to  the  dock.  Timber  and  long  pieces  which  could  not  be 
conveniently  taken  through  this  lock  were  admitted  through  the 
timber-lock. 

A  sand-pump  designed  by  Mr.  C.  W.  Clift,  master-machinist  of 
the  work,  operated  most  successfully,  proving  economical  both  to 
run  and  keep  in  repair,  and  effective  and  reliable.  An  almost  sphe- 
rical casting  was  formed  with  two  necks  diametrically  opposite  each 
other.  A  pipe  leading  to  the  suction-hose  screwed  into  the  lower 
neck,  its  upper  end  almost  entering  the  upper  neck.     Water  from  a 


Plate  XXIV. 


Plate  XXI. 


a.      c  ■ 
1     ,      c 


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41 ©- 


Plate  XXII. 


CrOM  and  Longitudinal  Section*-  Section  sheathed  and  teady  for  masonfy 
SHOWING  METHOD  OF  BUILDING  TUNNEL  THROUGH  SAND  -  NEW  YORK  SIDE. 


II       1       1       1 

1      1      1      II 

1      1      1       1      1 

1       1 

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1         , 

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111111/ 

[    I         l         1         1         1     | 

V\  l         l         1         1         1  / 

Vlli    ,? 

SHOWING  PROJECTION  OF  RINGS  OF  PLATES. -WORKING  IN  SAND. 


Plate  XXIII. 


Plate  XXV. 


W  ISM 


i  ■>!. ' 

SIZES  OF  IRON  PLATES 


END  ELEVATION  OF  IRON  BULKHEAD 


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ii  y 


TUNNELING   UNDER  THE   nUDSON    RIVER.  65 

pressure-pump  entered  at  the  upper  side  of  the  globe  and  was  con- 
ducted by  a  wide,  curved,  annular  flange  to  the  lower  part  of  the 
chamber  ;  it  then  turned  and  passed  between  the  end  of  the  suction- 
pipe  and  upper  neck,  and  thence  out  through  the  delivery-pipe.  The 
pump  worked  upon  the  principle  of  the  induced  current,  and  the  sharp 
sand  emerging  from  the  suction-pipe  struck  against  the  sides  of  the 
lower  end  of  the  delivery-pipe.  At  that  point  most  liable  to  vrear 
was  inserted  a  bushing  of  chilled  cast-iron,  above  which  was  a  piece 
of  composition  metal,  both  pieces  being  made  thicker  at  the  middle. 
These  were  cast  to  lit  the  pump  and  required  no  adjustment,  being 
held  in  position  by  a  screw-cap.  The  distance  between  the  top  of 
the  suction-pipe  and  the  delivery-pipe  could  be  regulated  by  screw- 
ing or  unscrewing  the  lower  pipe,  and  any  rate  of  discharge  could 
be  obtained  with  little  or  no  trouble. 

The  delivery-pipe  led  to  the  surface  of  the  ground,  and  the  suc- 
tion-pipe terminated  in  a  flexible  length  which  was  placed  in  the  box 
containing  the  water  and  sand  to  be  removed.  The  pump  would 
throw  out  fine  sand  or  coarse  gravel  and  any  stone  small  enough  to 
pass  through  the  piece  of  chilled  iron.  It  never  clogged,  and,  as  al- 
most all  the  wear  came  upon  the  chilled-iron  bushing,  the  cost  to 
keep  it  in  repair  was  but  trifling. 

The  lower  doors  of  the  supply  air-lock  opened  upon  a  platform 
built  in  the  working-chamber  and  extending  along  the  tunnels  to  the 
bulkheads  ;  from  the  other  side  of  the  bulkheads  the  platform  ex- 
tended to  the  headings.  Both  tunnels  were  left  a  little  more  than 
half-full  of  excavated  material. 

On  August  20,  1882,  a  blow-out  occurred  in  the  fifth  section  65 
feet  from  the  bulkhead  in  the  north  tunnel  (at  that  time  the  south 
tunnel  had  not  been  started).  The  section  was  15  feet  long,  and 
had  been  bricked  up  at  the  invert.  A  plate  was  forced  out  in  the 
iron  bulkhead,  allowing  the  air  to  escape.  The  air-pressure  at 
the  time  was  26^  pounds  per  square  inch.  The  plate  was  in  the 
fifth  row,  near  the  end.  The  workmen,  being  warned  by  the  pecu- 
liar hissing  noise,  had  ample  time  to  reach  the  lock,  which  was  ap- 
proached by  a  short  flight  of  steps. 

This  extra  long  section — 15  feet — required  more  than  the  usual 
time  to  build,  so  that  the  air,  under  the  high  pressure  of  28  pounds 
for  several  days,  found  avenues  of  escape  to  the  surface  along  the 


66  TUNNELING   UNDER   THE  HUDSON    RIVER. 

piles,  and  in  time  these  passages  became  enlarged  so  that  the  plates 
could  not  be  held  in  position,  and  hence  control  of  the  air  was  lost. 

The  flooded  section  was  entered  by  a  diver,  who  found  the  upper 
courses  of  plates  in  the  bulkhead  uninjured,  but  those  immediately 
adjoining  the  plate  at  which  the  leak  took  place  were  much  out  of 
place.  The  air  was  then  admitted,  when  the  water  was  expelled  from 
the  upper  part  of  the  section,  or  to  a  level  corresponding  with  the 
broken  plate.  This  was  sufficient  to  give  a  breathing-space  for  the 
men,  who  removed  the  distorted  plates  and  inserted  others.  This 
was  a  labor  of  exceeding  difficulty,  prosecuted  under  the  most  try- 
ing surroundings,  and  which  well  illustrates  the  courage  and  skill 
of  those  by  whom  it  was  accomplished.  It  took  45  days  to  recover 
what  had  been  lost  by  the  blow-out. 

Plate  XXI.  is  a  section  and  plan  showing  the  piles  met  in  pass- 
ing under  the  bulkhead-wall  (this  drawing  only  represents  10  lin- 
eal feet,  and  as  there  were  25  feet  in  all  some  idea  may  be  formed 
of  the  difficulties  encountered) ;  this  is  also  shown  in  the  longitudi- 
nal section,  Plate  XXYII.  Many  of  these  piles  extended  nearly 
through  the  tunnel,  and  they  not  only  had  to  be  cut  off,  but  provi- 
sion had  to  be  made  to  guard  against  any  subsequent  settlement. 

The  masonry  of  the  tunnel  was  made  2l/2  feet  thick,  and  was  laid 
in  Portland  cement  mixed  in  the  proportion  of  one  cement  to  two 
sand. 

During  the  month  of  May,  1883,  the  work  was  advanced  at  the 
average  rate  of  one-third  of  a  foot  per  day.  This  was  largely  due  to 
the  fact  that  the  calking  in  the  joints  of  the  iron  plates  was  forced 
outward  by  the  air,  and  thus  much  time  and  labor  were  required  to 
watch  for  and  stop  the  leaks.  The  angle-irons  were  riveted  flush  with 
the  four  sides  of  the  plate,  and,  as  a  consequence,  the  wet  silt-tamping 
put  between  the  flanges  formed  by  the  angles  was  blown  outward  by 
the  air-pressure  when  any  shifting  occurred  in  the  line  of  the  plate  ; 
if,  as  sometimes  happened,  the  plates  were  forced  up  slightly,  the 
joint  opened  outward  and  allowed  the  packing  to  escape.  This  was 
remedied  by  riveting  the  angle-irons  to  the  plate  in  such  a  manner 
as  to  break  joint ;  this  was  accomplished  by  allowing  two  adjoining 
angles  to  project  beyond  the  edges  of  the  plate,  while  the  two  remain- 
ing angles  were  set  back  from  the  edge  of  the  plate.  By  this  ar- 
rangement the  plate-joints  and  angle-joints  were  thrown  out  of  line, 


Plate   XXVI. 


bsmmM 


Plate   XXVII. 


LONGITUDINAL  SECTION.  PLAN    AND  CROSS   SECTION    THROUGH    BULKHEAD  -  NEW  YORK   SIDE 


LONGITUDINAL  SECTION  THROUGH  TUNNEL-NEW  YORK  SIDE.    Jolr  UB 


.ivxx  3t6iq 


n 


:« 


■ 


TUNNELING    UNDER  THE   HUDSON    RIVER.  07 

and  any  filling  placed  between  the  flanges  was  prevented  from  es- 
caping outward  by  the  projecting  plate.  After  this  method  was 
adopted  1  foot  of  tunnel  was  completed  each  day. 

About  75  feet  out  from  the  caisson  had  been  finished  when  the 
work  was  stopped,  November  5,  1882,  for  want  of  money,  and  water 
allowed  to  fdl  the  tunnels  and  caisson;  it  remained  in  this  condi- 
tion until  March  20,  1883,  when  steam  was  turned  on  and  com 
pressed  air  forced  in  again.  In  two  days  work  was  begun  at  the 
heading,  and  continued  until  July  20 — four  months— during  which 
time  72  feet  of  masonry  had  been  put  in  the  north  tunned,  and  the 
south  tunnel  had  been  cut  through  the  caisson  and  23  feet  of  it  com- 
pleted.    "Work  was  again  suspended  because  of  lack  of  funds. 

During  this  period  better  results  had  been  accomplished  than 
during  the  previous  year  ;  the  men  had  gained  experience,  and  all 
the  new  plans  worked  admirably.  The  average  rate  of  progress 
was  from  1  to  3  feet  of  completed  tunnel  per  day. 

"When  work  was  stopped  the  north  tunnel  had  been  carried  so 
far  as  to  be  nearly  out  of  the  sand.  Where  the  heading  now  rests 
the  upper  part  is  in  silt  ;  and  as  the  dividing  line  between  the  silt 
and  sand  extends  downward  very  sharply  (as  shown  in  Plate 
XXVII. ),  but  a  short  length  will  have  to  be  built  when  the  work 
can  be  prosecuted  entirely  in  silt.  This  wrill  be  a  great  aid  to 
rapid  work  in  the  future,  and  the  daily  progress  should  equal  that 
made  at  the  other  side  of  the  river. 


At  the  New  York  side  all  of  the  machinery  was  in  a  building 
located  a  short  distance  back  or  east  of  the  shaft.  The  plant  con- 
sisted of  two  air-compressors,  two  boilers,  engine  and  dynamo, 
pumps,  etc.  The  compressors  forced  the  air  into  an  iron  reservoir, 
from  whence  it  was  conducted  by  a  pipe  to  the  tunnels  ;  the  pressure 
was  indicated  by  a  mercury  -gauge  connected  with  the  reservoir. 

The  Clayton  duplex  and  double-acting  air-compressor  had  two 
steam-cylinders  22  inches  in  diameter,  two  air-cylinders  24  inches 
diameter,  the  stroke  being  30  inches.  It  was  designed  to  make  from 
70  to  80  revolutions  per  minute,  the  capacity  being,  by  measure- 
ment, 2,500  cubic  feet  of  free  air  per  minute.     The  tops  of  the  cross- 


68  TUNNELING  UNDER  THE  HUDSON   RIVER. 

heads  are  rigidly  connected  by  a  heavy  rod,  and  the  bottoms  by  a 
distance-piece  which  serves  as  a  slide,  working  on  a  long,  adjustable 
slipper-guide  placed  inside  of  the  frame,  and  by  its  use  the  cylin- 
ders are  relieved  from  all  weight  and  wear  excepting  that  caused  by 
the  piston-packing.  The  suction-valves  are  of  the  poppet  style,  and 
are  so  numerous  as  to  give  plenty  of  opening  for  admission  of  air 
until  the  cylinder  is  filled  to  almost  the  atmospheric  pressure  ;  they 
are  placed  in  the  air-cylinder  heads,  and  all  danger  of  their  falling 
into  the  cylinder  through  the  stems  breaking  or  nuts  coming  off  is 
overcome  by  bolts  which  effectually  prevent  the  valve  from  falling 
and  enable  the  replacing  of  the  nut  without  taking  off  the  head  ;  or, 
should  the  stem  break,  the  valve  can  be  fastened  against  the  seat 
until  it  is  convenient  to  repair  it.  The  discharge-valves  are  lifted 
by  an  adjustable  tripping  device  which  can  be  set  to  lift  at  any 
desired  point  in  the  stroke,  thus  affording  a  free  escape  for  the 
air  in  the  cylinder  as  soon  as  it  has  readied  the  working  pressure. 
The  cylinder  is  surrounded  by  a  water-jacket  so  constructed  as  to 
compel  the  water  to  circulate  from  the  centre  along  the  top  to  and 
around  the  ends  of  the  cylinder  for  one- fourth  of  its  length,  thus 
covering  the  points  at  which  the  greatest  compression  of  air  takes 
place,  and  at  which  the  most  heat  is  generated. 

The  steam  and  air  cylinders  are  securely  bolted  to  a  strong  bed, 
and  are  tied  together  by  wrought-iron  rods  ;  this  arrangement  ad- 
mits of  the  fly-wheel  being  placed  in  the  centre  of  the  machine, 
thereby  giving  compactness. 

In  the  Ingersoll  air  compressor  the  steam  and  air  cylinders  were 
16  inches  in  diameter  and  the  stroke  2-i  inches  ;  at  a  speed  of  88  re- 
volutions per  minute  the  actual  amount  of  air  was  368  cubic  feet  per 
minute.  The  frame  is  rectangular  in  form,  and  is  made  in  one  cast- 
ing, the  vertical,  parallel  sides  of  which  are  stiffened  by  transverse 
ribs.  The  air  and  steam  cylinders  are  in  line,  and,  with  two  heavy 
fly-wheels,  are  supported  on  the  frame,  making  it  impossible  for 
any  part  to  get  out  of  line.  Between  them  is  a  cast-steel  cross-head 
with  swivel-block,  into  which  piston-rods  are  fitted  and  held  by  a 
king-bolt  and  adjusting  clamp  ;  this  construction  permits  the  cross- 
head  to  adjust  itself  to  any  irregularity  in  the  length  of  the  connect- 
ing-rods. The  main  and  cut-ofi"  valves  are  operated  by  rocker-anna 
placed  at  the  rear  end  of  the  frame  back  of  the  shaft.     The  journal 


'ITNNKUNo    CTNDEE  THE   HUDSON    BIVEE.  69 

and  crank-pin  boxes,  slides,  Induction  and  eduction  valves  are 
made   of  phosphor-bronze!     The   induction-valves  are  cylindrical 

and  have  their  entire  circumference  for  a  wearing-surface  and 
guide;  they  work  in  cages  screwed  into  the  cylinder-heads  from 
the  outside,  and  project  beyond  the  cages  sufficiently  to  admit 
springs  between  a  rim  on  the  valves  and  the  face  of  the  cages. 
Cylindrical  balanced  eduction-valves  move  in  similar  cages,  and  are 
held  in  place  by  caps  bolted  to  the  outside  of  the  cylinder-heads, 
through  which  adjusting-screws  pass.  Each  valve  can  be  removed 
from  the  outside. 

Cooling  is  effected  by  a  small  double-plunger  pump,  worked 
from  the  cross-head,  throwing  water  into  the  cylinder.  An  auto- 
matic speed  and  pressure  regulator  is  located  on  the  air-cylinder  and 
connected  to  the  receiver  by  a  small  pipe. 

All  of  the  boilers  were  furnished  by  the  Erie  City  Iron-Works, 
of  Erie,  Pa.  There  were  two  on  the  New  York  side,  of  70  horse- 
power each.  The  dimensions  were  :  Diameter  of  boiler,  60  inches  ; 
thickness  of  shell  £!  of  an  inch,  of  head  ■&;  length  of  flues,  14  feet ; 
number  of  flues,  3  inches  in  diameter,  82  ;  square  feet  of  heating- 
surface,  1,050. 


After  mature  deliberation  the  writer  came  to  the  conclusion  that 
it  would  be  better  to  devote  a  page  or  two  to  those  who  at  various 
times  were  in  charge  of  the  tunnel  rather  than  attempt  to  mention 
them  as  the  description  of  the  work  progressed  ;  it  will  be  readily 
perceived  that  the  latter  plan  would  have  involved  needless  repeti- 
tion and  annoyance. 

At  the  beginning  Col.  W.  H.  Paine  was  consulting  engineer. 
In  November,  1879,  while  sinking  the  shaft,  Mr.  C.  C.  Brush,  of  the 
firm  of  Speilmann  &  Brush,  accepted  the  position  of  chief  engineer 
and  continued  in  charge  until  August,  1880.  Mr.  E.  H.  Burlingame 
was  assistant  engineer  and  continued  in  charge  after  this  period. 
Mr.  J.  F.  Anderson  began  his  connection  with  the  work  as  super- 
intendent while  the  bottom  of  the  shaft  was  being  put  in,  in  Decem- 
ber, 1879  ;  he  invented  the  pilot  and  remained  in  charge  until  Gen. 
Wm.  Sooy  Smith  assumed  control  of  the  engineering  department  in 


70  TUNNELING   UNDER  THE  HUDSON   KIVER. 

May,  1881.  One  year  later  Mr.  S.  H.  Finch,  who  had  been  assistant 
engineer  since  February,  1880,  took  charge  and  continued  until 
operations  were  suspended,  Mr.  C.  W.  Raymond  being  his  assistant. 
During  all  the  time  the  machinery  was  in  charge  of  Mr.  C.  W.  Clift. 


The  main  tunnel  under  the  river  will  be  5,500  feet  in  length,  the 
New  Jersey  approach  will  be  4,000  feet  in  length  and  the  New 
York  about  4,500  feet,  making  a  total  of  14,000  feet,  or  about  800 
feet  over  2l/z  miles. 

It  is  intended  to  have  not  less  than  12  feet  of  silt  between  the 
top  of  the  tunnel  and  water,  or  bed  of  the  river,  at  any  point. 

There  are  about  14  cubic  yards  of  excavation  for  every  lineal 
foot  of  single  tunnel ;  hence  for  5,500  feet  of  double  tunnel  154,000 
cubic  yards  would  have  to  be  removed. 

There  are  3,000  bricks,  6  barrels  of  cement,  and  1,200  pounds  of 
iron  plates  per  lineal  foot ;  hence  5,500  feet  of  double  tunnel  would 
require  33,000,000  bricks,  60,000  barrels  of  cement,  and  13,200,000 
pounds  of  iron.  These  estimates  are  for  the  main  tunnel  between 
the  shafts.  The  two  approaches  will  require  about  double  the  above 
quantities,  except  in  the  case  of  the  iron,  the  amount  of  which  will 
depend  largely  upon  the  method  of  construction. 

With  the  money  in  hand  to  finish  the  whole  it  is  estimated  that 
all  could  be  completed  in  two  and  one-half  years.  It  is  to  be  hoped 
that  a  work  of  such  magnitude  and  universally  acknowledged  pub- 
lic benefit  will  not  long  suffer  for  the  want  of  the  necessary  means 
to  complete  it. 


1NGERS0LL  ROCK-DRILL  GO. 

lO  PARK  PLACE,  NEW  YORK. 


IMPROVED  "STRAIGHT-LINE"   SINGLE 

AIR  -COMPRESSOR 

SAME  AS  FURBISHED  FOR  THE  HUDSON  RIVER  TUNNEL. 

Unequalled  m  Efficiency,  Economy,  and  Durability,  Fon  the  Transmission  of  Power  in 
Mines  ok  Tunnels  TO  RUN  ROOK-DRILLS,  COAL-CUTTERS,  PUMPS,  and  every 
variety  of  Machinery  underground,  at  lontc  or  short  distances,  and  wherever  the  direct  use  of  Steam  is  not 
practicable  or  convenient  ;  for  Driving  Tunnels  by  THE  Pskumatic  Sv-tkm,  for  Sinkino  Bridge-Caissons, 
etc.,  etc. 

The  Principal  Points  of  Superiority  of  the«e  Compressor*  are: 

1st.  Minimum  of  loss  due  to  clearance  and  increase  of  temperature  "luring  compression. 

2d.  Direct  strains  and  direct  application  of  power  to  overcome  resistance. 

3d.  Consequent  economy  in  the  use  of  power, 

4th.  Water-injection  for  cooling,  lubricating,  and  packing  clearance  and  dead  spaces. 

5th.  Dry  air  and  reduced  liability  to  freezing. 

Cth.  Improved  induction-valves.  Insuring  complete  filling  of  the  cylinder  with  air  at  atmospheric  pressure. 

7th.  Balance  discharge- valves,  requiring  slight  excess  of  pressure  to  open. 

8th.  Simple  and  efficient  automatic  regulation  of  speed  and  pressure. 

9th.  In  design,  strength,  compactness,  durability,  workmanship,  and  material. 

ALSO, 

SINGLE    AND    DUPLEX    COMPRESSORS 

FOR  STEA'M  AND  WATER  POWER.  HIGH  OR  LOW  PRESSURE. 


EVGERSOLL  IMPROVED   "ECLIPSE"  ROCK-DRILLS, 

Decidedly  the  most  Effective,  Simple,  Durable,  and  Economical, 
a><> 

ALL  KINDS  OF  MACHINERY  AND  APPLIANCES  FOE 

Mining,  Tunneling,    Grading,    Quarrying, 

Submarine  Drilling,  and  Rock  Excavations  in  general. 


Estimates  Furnished  for  Complete  Plants. 
SEXD  FOR  FULL  DESCRIPTIVE  CATALOGUE. 


ROCK-DRILLS  AND  GENERAL  MIXING  MACHINERY. 


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Used   in  many  of  the  principal  GOLD,  SILVER,  COPPER,  COAL,   AND   IRON 
MINES  in  North  and  South   America. 


SIMPLE I      DURABLE I I      ECONOMICAL  1 1 1 


Portland (HW  Cement. 


General  Selling  Agents,  91  Liberty  Street,  New  York. 

Office  of  the  Hudson  Ti  nnel  Construction  Co., 
New  York,  February  27th,  1883. 
Messrs.  Johnson  &  Wn  SON— Dear  Sn:<  :  In  the  construction  of  our  Tunnel  thus  far  we  have  used  many 
thousand  barrels  of  your  -  ut,  and  have  universally  found  it  equal  to  the  beat  brands  of 

foreign  cement.    In  fact,  we  ask  for  nothing  better,  and  shall  continue  its  use  where  a  superior  quality  of 
cement  Is  required. 

We  can  show  j  ou  excellent  samples  of  its  strength  and  general  character  at  anytime.     Trusting  you  may 
furnish  as  good  an  article  in  the  future  as  in  the  past,  I  Ihl,'  to  remain,  yours  respectfully, 

D.  C.  HASKIX,  Manager. 


ESTABLISHED    1856. 


»J 


NT  CO 


MANUFACTURERS   OP 


TRADE        /A\        MARK. 


ROSENDALE 

HYDRAULIC 

CEMENT. 

This  Cement  is  a  superior  article,  being  very  uniform  in  quality  and  fineness.    It  was  used  very  largely  in 
the  construction  of  the  Hudson  River  Tunnel,  and  received  the  highest  commendation. 
Prices  and  other  information  will  be  f uruished  ou  application  to 

H.  R.  BRIGHAM,  Secretary, 

95  Liberty  Street,  New  York. 

iii 


J.    £\    ANDERSON. 


O.    C.    38A3R3Et. 


ANDERSON  &  BARR, 


(ATCaAFAtAT*  BEIJIC*.  TM* 


ENGINEERS  AND  CONTRACTORS, 


SPECIALTIES  : 


PNEUMATIC  WORK, 
DEEP  FOUNDATIONS, 


Automatic   Dredge   for 
Sinking  Cylinders. 


AND 


Tunneling  in  Soft  Materials. 


Control  the  Patents  for  the  Automatic  Dredge  and 
Anderson  System  of  Tunneling. 


Address 


ROOM  12,  TRIBUNE  BUILDING,  N.  Y. 


IV 


ALEXANDER  rOLLOCK,  Prks.  JOSEIMI  Q.  HAURISON,  THUS.  WM.  H,  IIAKWW.N,  Bao. 


JFhe  Tabular  Barrow  and  Machine  Gs., 

169,  171,  173,  and  175  FOURTEENTH   STREET, 
J3SH.S3Er5r   CIT-5T,    N.    «T. 


Patent  Tubular  Wheelbarrows, 
Patent  Eureka  Steam -Hammiik-, 
furnace-charging  barrows, 
Coax,  and  Coke  Cars, 

Portable  Hoisting-Winches, 
Duiffei.  Blowers, 
Machine  Work, 


Lasher's  &  Jones'  Patent  Piston  Bfkdtob, 
Roofer's  Tar-Boilino  Ketti.es, 
Coal  and  Ash  Buckets, 
Sheet-iron  Work, 
Coaling-Tubs, 
Forcings, 
Etc.,  Etc. 


Contractors  for  the  Iron- Work  used  in  the  Construction  of 
the  HUDSON  TUNNEL. 


RAILROAD  GAZETTE  PUBLICATIONS: 

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free. 


K  1  1  fj  1^    mailed  on  receipt  of  price  by  The  Railroad  Gazette,  73  Broadway,  New  York  : 


Car-Builders'  Dictionary,  new  edition $3  00 

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Recent  Locomotives  (reduced  price,  50  cents  ex- 
tra for  postage) 3  50 

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We  publish  each  week  in  The  Railroad  Gazette  valuable  practical  articles  on  every  branch  of  Rail- 
road Engineering,  Mechanics,  and  Operation.  Mr.  Charles  Paine  continues  his  series  of  valuable  articles, 
the  subjects  of  his  later  treatises  being  "Shops,"  "Engine-Houses,"  "Telegraphs,"  "Fences,"  "Locomo- 
tives," "Cars."     >To  engineer  should  fail  to  read  these  papers. 

THE  RAILROAD  GAZETTE, 

73   Broadway,  New  York, 


IKDEX    TO    ADVERTISEMENTS. 


TABM 

Anderson  &  Barr iv 

Clayton  Air-Compressors i 

Iludson  River  Cement  Co ii 


Ingersoll  Rock-Drill  Co. 


Railroad  Gazette  Publications v 

Savior's  Portland  Cement i ii 

Tubular  Barrow  and  Machine  Co v 


